Courier Mail Server

NOTE: a more readable HTML version of this INSTALL document can be found in courier/doc/install.html.

Installation

Building rpm and deb packages

These are not the same packages as the ones from various distributions' repositories. These packages carry a higher internal revision level in order to prevent them from getting upgraded by the distribution packaging. These packages exist in order to have a convenient way of updating after a release without waiting for the distribution's package to get built.

NOTE: If a distribution package is already installed it should be removed completely before switching to the upstream version (dnf remove or apt purge). Preserve any existing configuration files, beforehand, in order to restore it after switching packages. This applies to all Courier packages. A switch to this courier package requires switching the courier-unicode and courier-authlib packages too.

NOTE: These packages use their own, generic, installation layout that may deviate slightly from the package installation conventions preferred by the distributions:

The main "courier" package starts all modules, whichever modules are installed. Depending on the distribution installing the main "courier" package may or may not automatically start it. Installing or uninstalling an additional package with a service may or may not result in an appropriate restart.

rpm

Run dnf install rpm-build if it's not installed already, then:

rpmbuild -ta courier-version.tar.bz2

If this fails due to any missing dependencies, install them. This will eventually create source and binary RPM packages. This works for all Courier packages.

Changing the options that the RPMs are built with

Building the RPMs directly from the source tarball uses the default options programmed into the tarball. Sometimes you may want to use different options. For example, you might want to enable fixes for certain bugs in some IMAP clients. Use the following procedure to build the RPMs with different options:

Building DEB packages

Create an empty directory and copy/move the tarball into it:

$ mkdir tmp
$ mv courier-VERSION.tar.bz2 tmp
$ cd tmp

Unpack the tarball and cd into the unpacked subdirectory:

$ tar xvf courier-VERSION.tar.bz2
$ cd courier-VERSION

Run the courier-debuild script, which is a wrapper for debuild, and forwards its parameters to it:

$ courier-debuild -us -uc

NOTE: the above steps must be followed strictly. The courier-debuild script expects the distributed tarball in its parent directory.

This eventually produces a deb subdirectory with .deb packages that can be installed with "dpkg -i".

NOTE: All Courier packages should be built with the same version of gcc, which is selected by the DEBGCC environment variable before running courier-debuild. See courier-unicode's INSTALL for more information.

Maintainer Mode (see README in the git repository to set up)

make rpm or make deb, as appropriate, will:

  1. Increment an internal release number.

  2. Run make dist.

  3. Proceed and build a new release, creating the native packages in the rpm or deb subdirectory.

Manual installation

NOTE:

This documentation describes manual installation of the Courier mail server. This is a somewhat involved process that may overwhelm people that do not have prior experience with installing large software packages. Many distributions have a separately-maintained, preconfigured, ready-to-install packages that can be loaded with much less investment of time. Installing a pre-built package would probably be the best approach in this case.

Should you choose to install a platform-specific prebuilt package, you should carefully read any custom documentation files that are included in the package. Most platform-specific packages provide custom, non-default configuration settings that are optimized for that platform's unique policies. Feedback about platform-specific precompiled packages should be copied to the development group that maintains the package, in additional to the platform-neutral courier-users mailing list.

Read this document in its entirety before entering a single command. Installing the Courier mail server for the first time will take a while. If possible, consider looking around for anyone who has already packaged the Courier mail server for your operating system, and save yourself the hassle.

Fortunately, it gets easier with each subsequent installation. The Courier mail server is a complicated piece of software. Most problems people will have are likely to be with the configuring and installing it correctly. Designing complex software that compiles and installs on a wide variety of POSIX systems is not a trivial task.

The Courier mail server's configuration and installation scripts are very flexible in setting up installation directories for each logical set of files - configuration files, binaries, scripts, the mail queue, and more. If you begin by installing someone else's package, instead of installing everything yourself, you should take careful notes where things are installed. If you later decide to roll your own package, you will either need to use a COMPLETELY IDENTICAL configuration, or take care to back up your old configuration, and then restore it after the upgrade. The following documentation refers to the default location of various configuration files (and other files as well). If you choose to install some files in a non-default location (either by yourself, or by using someone else's package), you will need to take this into account while reading the following documentation.

This cannot be emphasized enough: the configuration defaults are very generic; the goal is to have the default configuration settings work for almost everyone. In every case using at least a couple of non-default parameters will make the Courier mail server work better on your system. You should anticipate going through several trial-and-error installs, tweaking the options to see what works better for you.

NOTE: older versions of the linuxconf configuration tool are hardwired for sendmail. They like to change the permission of the sendmail wrapper to match the permissions they think the real sendmail should have. Older versions of linuxconf also have a tendency to create the /var/spool/mqueue directory, even if sendmail is not installed.

Table Of Contents

The following table of contents might look intimidating at first, but some sections are marked "optional". These sections are not required for a basic installation as a simple ESMTP server.

Upgrading an existing installation

Upgrading from the Courier mail server 1.0.16 or earlier

The IMAP server switched to using the inotify kernel API directly instead of the legacy FAM/Gamin daemon. When using virtual mail accounts it will be necessary to increase the kernel's configured limit on the maximum number of inotify file descriptors, see the IMAP server configuration notes, below.

Upgrading from the Courier mail server 0.73.1, or earlier

The unicode library in Courier is now a separate package. Download the Courier Unicode Library before updating to 0.74, or later.

Upgrading from the Courier mail server 0.72, or earlier

Version 0.73 removes the TLS_DHCERTFILE parameter from esmtpd, esmtpd-ssl, imap, and pop3d configuration files. DH parameters, and DH parameters only, get read from the new TLS_DHPARAMS file (and the other functionaly of TLS_DHCERTFILE, for DSA certificates, is merged into TLS_CERTFILE). After upgrading, run the mkdhparams script to create a new TLS_DHPARAMS file.

Upgrading from the Courier mail server 0.66.3, or earlier

In 0.67, the IMAP server resets the epoch for an internal sequence number generator for new mailboxes. This is an internal attribute of individual IMAP folders, that's defined by the IMAP specification. Each folder in a mailbox carries an individual sequence number, it is defined as a 32 bit integer value, and required to be a monotonically increasing value. and RFC 2060 recommended that "... a good value to use for the unique identifier validity value is a 32-bit representation of the creation date/time of the mailbox."

On modern platforms, the system time is now a 64 bit value (even on the remaining 32 bit platforms). With Y2038K on the horizon, it's time to reset the epoch (the new epoch, for anyone who cares, runs until the year 2069). The upgrade impact on existing systems is as follows.

There is no impact on existing folders in existing mailboxes. New folders will have their internal sequence number in the new epoch.

One potential issue exists if a folder gets deleted by the IMAP client, and then recreated later. The new folder will now get a lower sequence number. Although this is technically not allowed, it's unlikely to cause problems with most IMAP clients. If the same IMAP client deletes and recreated the mailbox, the client should be completely up to speed. If, however, there's an IMAP client that accesses the same folder, and some other IMAP client deletes and recreates the same folder, this might cause confusion. Most IMAP clients are likely to recover automatically; most IMAP clients only care that the new sequence number they see is different from the previous one, in order to trigger a full resynchronization with the server. In case an IMAP client fails to resynchronize, the remedy is to remove the IMAP account configuration from the client, and add it back in.

Copying a mailbox by directly copying the files in maildirs preserves each folder's epoch. However if a mailbox gets migrated by copying its contents over IMAP, the folders on the destination IMAP server will not necessarily have a monotonically higher value -- neither does IMAP guarantee that different IMAP servers must be in agreement with each other on the subject of sequence numbers -- and if IMAP clients are repointed to a new server they may experience problems opening existing mailboxes. To remedy this situation it will be necessary to completely remove and then reconfigure the IMAP account, in the IMAP client. Again, verbatim copying of maildirs has no issues.

A marginal situation exists where if a server completely runs of disk space, or if there's a hardware failure, and the IMAP server is unable to retrieve or save an existing folder's sequence number, and must now start afresh and generate a new one, the IMAP server running on a new epoch will recover with a lower sequence than the one that existed before. The rememdy is the same: remove the IMAP account configuration from the client, and then recreate it.

Upgrading from the Courier mail server 0.63.0, or earlier

There's a new setting, SYSLOCALE, in the courierd configuration file, which initializes the environment from the default system locale. The configuration script heuristically searches for a list of known locale initialization scripts on various platforms, if found.

If your platform's locale configuration script's name is not known to the configuration script, manually specify your default system locale in this configuration setting.

Upgrading from the Courier mail server 0.55.1, or earlier

The webmlmd tool has been significantly enhanced, with a new administration screen that consists of three new template files: style.css.tmpl, webmlmlistadmin.tmpl.html, and webmlmlistadminpw.html.html. These three template files must be installed in each mailing list directory. You may copy them manually, or use the couriermlm update command. couriermlm update overwrites all your list-specific customizations, so make backups first!

Upgrading from the Courier mail server 0.54.2, or earlier

The logic for outbound authenticated SMTP has changed. This is when the Courier mail server sends outbound mail through a smarthost that requires authentication.

The specified smarthost's name is still looked up in DNS, as before. When smtp.example.com is specified as the smarthost's name, The Courier mail server looks up any MX or A records for smtp.example.com. A connection gets established to a server whose name may be different than the original DNS hostname, if it gets redirected via an MX or a CNAME record.

In earlier versions of the Courier mail server, the smarthost's userid and password must be listed using the resulting server's physical, resolved name. Starting with version 0.55, the smarthost's original DNS name must be listed instead. In all cases now, the name of the server listed in esmtpauthclient will now match the name specified in esmtproutes.

After updating to 0.55, the contents of the esmtpauthclient configuration file may need updating.

IMPORTANT: After updating to 0.55, all existing couriermlm mailing list directories must be updated with new configuration files. See the "update" command in the "MANUAL COMMANDS" section of the couriermlm(1) manual page. If you run many mailing lists, you are strongly advised to install the new version of the Courier mail server on another machine and become re-acquainted with couriermlm's configuration. In an emergency, make a backup copy of the couriermlm command from your existing version of the Courier mail server, before installing this update.

Upgrading from the Courier mail server 0.51, or earlier

Version 2.0 of maildrop, in the Courier mail server 0.52, introduces a new pattern matching engine that uses the PCRE library, that uses a completely different syntax. However, very few changes should be required to upgrade existing maildrop recipes to the new syntax.

After upgrading from the Courier mail server 0.51, or earlier, review the maildropfilter manual page which has been revised to document the new pattern matching syntax. The legacy pattern matching engine is still available by setting MAILDROP_OLD_REGEXP to 1. See also the "Conversion of maildrop 1.x pattern to 2.0" section in the manual page, for more information.

Upgrading from the Courier mail server 0.49.0, or earlier

couriermlm's default configuration now treats both the userid and the domain portion of E-mail addresses as case-insensitive.

Any existing mailing list that has subscribers whose E-mail addresses contain uppercase addresses must explicitly set the new CASESENSITIVE=1 list option, using the couriermlm command, otherwise those subscribers will have problems unsubscribing or posting messages to the list.

Upgrading from the Courier mail server 0.48.2, or earlier

The Courier mail server's default configuration now includes backscatter suppression. Review Backscatter suppression, below, for any needed configuration changes.

Upgrading from the Courier mail server 0.47, or earlier

Beginning with 0.48, the authentication library that used to be a part of the Courier mail server's source has been spun off into a standalone authentication library.

You must download and install the Courier mail server authentication library from https://www.courier-mta.org/authlib/ before upgrading. Review the documentation in the courier-authlib package for more information.

As part of installing courier-authlib, the configuration files in the Courier mail server's configuration directory that relate to authentication will be copied to courier-authlib's configuration directory. The files are: authdaemonrc, authmysqlrc, authpgsqlrc, authldaprc, and userdb (together with the .dist versions). This works only as long as the Courier mail server was installed in one of the known default installation directories. The documentation in courier-authlib explains what to do if the existing version of the Courier mail server is installed in a non-default location.

In any case, after upgrading to 0.48 these configuration files in the Courier mail server's configuration directory will no longer be used. To avoid future confusion the old copies of these configuration files (including the .dist files), should be removed from the Courier mail server's configuration directory. They now live in the Courier mail server-authlib's configuration directory (/usr/local/etc/authlib, or whatever was specified to the Courier mail server-authlib's configure script).

Upgrading from the Courier mail server 0.45.4 or earlier

The command to start the webmail server daemon has changed. The system startup script must be modified to run the new command: "/usr/lib/courier/sbin/webmaild start". Additionally, this scripts also starts pcpd, if required. It is no longer necessary to start pcpd by hand.

Upgrading from the Courier mail server 0.44.0 or earlier

Version 0.44.1 introduced an updated webmail implementation. The suid cgi-bin binary has been replaced by a combination of a stub and a daemon process. After upgrading to 0.44.1 you will need to modify your system startup script to run /usr/lib/courier/libexec/courier/sqwebmaild start. See below for more information.

Upgrading from the Courier mail server 0.42.2 or earlier

After upgrading from the Courier mail server 0.42.2, or earlier, any existing mail in POP3 mailboxes may show up as new mail, by some mail clients. This is a one-time event.

Upgrading from the Courier mail server 0.42.0 or earlier

Version 0.43 introduced some functional changes to the LDAP, MySQL, and PostgreSQL authentication modules. A new DEFAULTDELIVERY setting is added to each module, incorporating some functionality previously done by the MAILDIR setting. Previously, MAILDIR served two purposes: 1) define the default location to the primary mailbox, relative to the account's home directory, 2) provide default mail delivery instructions, overriding DEFAULTDELIVERY in the courierd configuration file.

Starting with this version, MAILDIR only specifies the default location for the primary mailbox, and this setting is now used only by the POP3, IMAP, and Webmail servers. The new DEFAULTDELIVERY setting specifies the default mail delivery instructions. Sites that previously used MAILDIR may now need to copy its setting to DEFAULTDELIVERY.

Upgrading from the Courier mail server 0.34.1 or earlier

Version 0.35 introduced the ability to update system passwords from the webmail server. If you are using the authuserdb authentication module, rerun the makeuserdb script after upgrading to 0.35 or later.

Prior to 0.35, the default configuration of the webmail server maintained a separate webmail password file. The webmail server did not have the logic to update system login passwords, the approach was to copy system login passwords into a webmail password file. Changing the webmail password involved simply updating the webmail password file, and life was good.

In 0.35, logic was added to update the real system password file, and the eliminate the webmail password file. After upgrading in 0.35, it will probably be necessary to reset all mail account passwords on existing accounts, since the webmail password file is not being used any more, and most people have probably changed their webmail passwords.

As the result of the password change, the default configuration script will now always build the authdaemond authentication module by default. Previously, authdaemond was built by default only if LDAP or MySQL support was necessary.

Upgrading from the Courier mail server 0.29.1 or earlier

Version 0.30 changed the format of most configuration files. The new configuration file format allows configuration files to be automatically upgraded. The automatic upgrade feature requires that both the old and the new installation have preformatted configuration files. Therefore, when upgrading from version 0.29.1 or earlier, use the following procedure to upgrade the existing configuration files.

All configuration files are installed in the same directory, "sysconfdir". sysconfdir is a configurable parameter, it's usually /usr/lib/courier/etc. sysconfdir is /etc/courier in the RPM and the DEB version of the Courier mail server.

Back up your existing sysconfdir

Make a backup copy of your current sysconfdir, then delete the old version of the Courier mail server. "rm -rf /usr/lib/courier" will do nicely. All the possible configurable settings are in sysconfdir, everything else can simply go.

Back up your existing sysconfdir

Make a backup copy of your current sysconfdir. The upgrade process reinstalls several default configuration files; specifically sysconfdir/aliases/system and sysconfdir/smtpaccess/default. Any additions to these files will normally be lost in the upgrade, and can be restored from the backup afterwards. Don't forget to rerun makealiases and makesmtpaccess.

Install the new version

Follow the installation procedure in the next section (including the make install-configure). The following configuration files are now preformatted for automatic installation:

   ldapaddressbook
   esmtpd
   esmtpd-msa
   courierd
   pop3d
   pop3d-ssl
   imapd
   imapd-ssl
   ldapaliasrc
   authldaprc
   authmysqlrc
   authpgsqlrc
   authdaemonrc

NOTE: depending upon your configuration, you may not actually have every one of these files installed, so just disregard the ones that are not present. Manually edit filename, and retype any custom modifications from the backup copy of the configuration file. This is a hassle, but it only needs to be done once. Future upgrades will be 99% automatic.

Any custom configuration changes are generally confined to these configuration files only. Very rarely are any configuration changes made to the remaining configuration files. If necessary, they can simply be restored from the backup copy made in the previous step. Something to keep in mind is that future versions may add additional complexity to other configuration files, resulting in additional configuration files being reformatted for automatic upgrading.

Overview

You will need the following software in order to compile and install the Courier mail server:

  1. The Courier Unicode Library

    The courier-unicode package must be installed and configured prior to installing the Courier mail server. Download the courier-unicode package from https://www.courier-mta.org/unicode/.

  2. The Courier mail server Authentication Library

    The courier-authlib package must be installed and configured prior to installing the Courier mail server. Download the courier-authlib package from https://www.courier-mta.org/authlib/.

  3. A C++ compiler

    The Courier mail server is primarily developed and built with gcc. Other C++ compiler may or may not work. Solaris's C++ compiler is reported to work without any problems. There are some issues with AIX's xlC compiler, which mostly has to do with the C++ libraries and header files. IBM has released a GNU/Linux development toolkit for AIX, which may help in getting the Courier mail server to compile.

  4. PCRE

    The PCRE2 library (http:/www.pcre.org) is required.

  5. wget

    The wget command must be installed.

  6. GNU IDN library

    This library (http://www.gnu.org/software/libidn/) implements support for internationalized domain names.

  7. GNU make

    On the BSD platform family GNU make is usually installed as gmake. Simply replace 'make' with 'gmake' in the following instructions. GNU make is REQUIRED. Use anything else at your own risk.

  8. Perl 5

    A recent version of Perl needs to be installed.

  9. GDBM or Berkeley DB library

    Either library must be installed.

  10. OpenSSL or GnuTLS

    Support for SSL/TLS requires OpenSSL/GnuTLS. All features that require SSL/TLS are disabled unless OpenSSL or GnuTLS is installed.

  11. OpenLDAP

    Support for LDAP directory services requires OpenLDAP client libraries to be installed. If OpenLDAP is not installed LDAP directory features are disabled. Sometimes there's some confusion when commercial LDAP servers are used, which come with their own development toolkits, which use a different API than OpenLDAP. Even if a commercial LDAP server is used to provide LDAP services, OpenLDAP is still required to enable LDAP services in the Courier mail server. Also, note that you need OpenLDAP development libraries and files. On most systems, the development files are packaged separately, in addition to the runtime OpenLDAP libraries. Make sure that you have not just the runtime OpenLDAP libraries installed, but the development libraries as well.

    Most of the LDAP support code is already provided by the Courier mail server authentication library. Some LDAP features, such as LDAP-based mail aliases, are implemented in the Courier mail server directly. OpenLDAP client libraries must be installed. If OpenLDAP is not installed, LDAP directory features are disabled.

  12. mgetty+sendfax, groff or troff (not tested), ghostscript, and NetPBM

    This optional software is required to send E-mail messages via fax. The Courier mail server will compile and install without this software, but you will not be able to send faxes. All packages must be installed prior to installing the Courier mail server, and binaries from all packages must be installed in the default PATH before running the Courier mail server's configure script.

    mgetty+sendfax, ghostscript, and groff, are required for basic fax support, which supports faxing of plain text, Postscript, and PDF-formatted content. It's probably possible to use the original UNIX troff instead of groff, but this has not been tested. Installing NetPBM adds the ability to fax GIF, JPEG, and PNG images.

The typical sequence of commands to install the Courier mail server is as follows. Read the following section before running these commands:

   ./configure [options]
   make
   make check       # Optional -- see below
   make install
   make install-configure

These commands are described in greater detail in the following sections.

If you're using gmake (the make on GNU/Linux, and gmake everywhere else), and you are compiling the Courier mail server on a workstation with multiple CPUs and plenty of memory, set the following environment variable:

   MAKEFLAGS="-j 4"; export MAKEFLAGS         # Bourne or Korn shell
or: 
   setenv MAKEFLAGS="-j 4"                    # The C shell

This must be done before running the configure script. This works only with gmake.

The Courier mail server will not work on a Linux kernel that's been patched with the Openwall security patch in its default configuration. The current version of the Openwall patch has a non-default option that turns off the portion of the Openwall patch which prevents the Courier mail server from running.

NOTE: Linux-Mandrake includes the Openwall patch in the alternative "secure" kernel package. The Courier mail server will not run on Linux-Mandrake under the alternative "secure" kernel. This package must be removed and the standard kernel package must be installed.

Preparing for installation

The first step consists of gathering some information about your existing mail system. Before proceeding, you will need to identify and resolve the following issues:

The Courier mail server can be used as a simple mail relay -- which does not store any mail locally but is merely a gateway between internal and external mail systems. The Courier mail server can also be used as a traditional mail server, accepting and storing messages in individual mailboxes that are accessible via POP3, IMAP, or webmail.

The Courier mail server defaults to storing mail in maildirs, not traditional flat file mailbox files. Maildirs require less I/O and CPU resources; they do not use locking; and multiple clients can read and write from maildirs simultaneously. Maildirs scale very well to servers with multiple CPUs. Some benchmark numbers on maildirs are available from https://www.courier-mta.org/mbox-vs-maildir/.

Additionally, The Courier mail server's integrated POP3, IMAP, and HTTP/webmail servers support maildir mailboxes only. They do not support mailbox files.

If you have an existing mail server in service, chances are that your current mail server delivers mail to mailbox files. You should consider migrating and converting to maildirs, but this will require that you also upgrade your POP3 server, your IMAP server, and all your other mail clients to software that supports maildirs. Fortunately, The Courier mail server already includes a fully integrated POP3 and IMAP server.

Still, if circumstances absolutely require for you to stick with mailbox files, The Courier mail server has limited compatibility support for delivering mail to mailbox files, but you have more homework to do:

If you decide to stick with mailbox files, you must know - of course - where your mailboxes are located, and what locking mechanism is being used by your mail software. Mailbox files require some form of locking, because only one application can access the mailbox file at the same time. Unfortunately, different operating systems use different locking methods. There are several possible locking strategies that can be used: so-called "dot-locks", or one of three possible kinds of file locking calls. You will need to consult the documentation for your existing mail software to determine what locking mechanisms you should use.

In most cases, mailbox files are located in a separate partition, usually the directory /var/spool/mail. In some instances, mailbox files may be kept in the home directory of each individual account, and the mail is delivered to either $HOME/Mailbox, or $HOME/INBOX. Again, you will have to figure this out by yourself.

The Courier mail server can deliver mail to mailbox files only if the default mailbox file is in the home directory of each individual account, and if you use file locking. The Courier mail server does not support dot-locks, and the Courier mail server does not support a separate mail directory for mailbox files. Mailbox files must be located in the home directory of each individual account.

The Courier mail server can use a recipient database (userdb) that can specify a non-default location for a recipient's mailbox. In theory, it is possible to point each account to its individual mailbox in /var/spool/mail, or somewhere else. However, that's a tedious task that must be done manually for each account, and is likely to be a major maintenance issue.

A better solution is to use a separate local mail delivery agent. Your existing mail system is very likely to include a separate local mail delivery agent. If you already use a mail delivery agent such as procmail, you probably already have it set to use the correct locking mechanism for mailbox files, and it already knows where the mailbox files are. The Courier mail server will be happy to hand off all local mail to procmail, or anything else for the actual delivery.

The Courier mail server source distribution includes the maildrop mail delivery agent which has some additional file locking options, however you'll have less problems if you stick with procmail in the beginning, and switch to maildrop after you've gained some experience configuring and installing the Courier mail server.

You should create a new userid and groupid named "courier". That's optional, but highly recommended. If this is not done, The Courier mail server will install as user/group daemon (or some other suitable user/group id). Only two of the Courier mail server's daemon processes run as a superuser (and one of them is perpetually waiting for a non-superuser daemon process to terminate, in order to restart it). Everything else runs as a non-superuser process. Ideally, you should reserve a separate user and group ID for the Courier mail server's use only, so a compromised mail system cannot be used to compromise the rest of the system. If push comes to shove, you can set up the Courier mail server to use a well-defined existing user and group ID, such as daemon.

The Courier mail server, by default, installs in /usr/lib/courier. Everything goes in there: binaries, scripts, configuration files, and manual pages. You will have to configure your man command to look for manual pages in /usr/lib/courier/man by adding this directory to the MANPATH environment variable. You will also need to add /usr/lib/courier/bin and /usr/lib/courier/sbin (for the root user only) to the default PATH. The Courier mail server's RPM and DEB packages install a script that automatically implements that.

Note that this installation layout is nothing more than a basic default, chosen because this simple arrangement works for everyone. The installation layout can be easily changed. For example, binaries can go to /usr/local/bin, and configuration files to /usr/local/etc. But keep in mind that the Courier mail server consists of several hundred individual files (at the last count), so if you install the Courier mail server somewhere else it might be very cumbersome to keep track of where everything went, and it will lead to almost guaranteed problems later, when you upgrade.

You should try to use some kind of a packaging system in order to keep track of your the Courier mail server installation. Once you choose a packaging system, you should stick to it. If you switch to a different packaging system you should take extreme care to remove your previous package, and install your new package. Extreme configuration flexibility means that different packages will install in different places, and even have different file ownerships!

For example, The Courier mail server's source code tarball can be built into a binary RPM package. The binary RPM package installs configuration files in /etc/courier, the mail queue in /var/spool/courier, and everything else in /usr/lib/courier. If you install this package, and later decide to either create your own package or use someone else's, you will have to make sure to use the same settings, or remove this package completely, before installing your new package. I mean it when I say "remove my package completely". That includes the mail queue containing any unsent messages. The Courier mail server will not function if it's reinstalled using a different user/group ID, or if you use a different value for any other option.

Once these issues are squared away, you are ready to configure and install the Courier mail server.

OPTIONAL: Install the Socks 5 client toolkit

The Courier mail server has the ability to send outgoing SMTP mail through a Socks 5 proxy. The Socks 5 proxy option requires a separate module, the Socks 5 client/server proxy to be installed before installing the Courier mail server. Download the Socks 5 proxy client library from https://www.courier-mta.org/download.html#sox and follow its installation instructions.

NOTE: Be sure to read the README, NEWS, and INSTALL files in the Courier mail server Socks 5 library toolkit, before attempting to install it for the first time (unless using the RPM or DEB build method).

Socks proxying must be implemented in relatively low-level manner, and may not work on all operating systems. This is why it is packaged separately, in case that it doesn't work. The configure script, described in the following section, enables Socks 5 support automatically if the Courier mail server Socks 5 proxy client library is already installed. To make sure that the library is installed correctly, specify the "--with-socks" option to the following configure script. This option aborts the configure script if it does not detect the Courier mail server Socks 5 proxy client library.

Run configure

After you are squared away with the preliminaries, run the configure script:

./configure [ options ]

NOTE

You MUST run the configure script as normal user, not root. Did you extract the tarball as root? It won't work. Delete everything you have just extracted, as root. Log in as a normal user. Extract the source code as a normal user, then run configure. You will do everything as a normal user, except for the final step of installing the compiled software. When you're ready to do a make install, later, su yourself to root, and run make install.

The configure script can take a while to complete. There will be more then thirty separate configuration scripts that will be executed by this command. To an untrained eye it may seem that the same configuration script is stuck in a loop; that's because all these configuration scripts share a lot of code. It may take as much as 15-20 minutes for configure to finish on a slow machine - even more.

You must have the uux command in your default search path if you intend to use the Courier mail server to relay mail via UUCP. You may need to modify your PATH environment variable to include the directory containing uux.

gcc/egcs is officially blessed for building the Courier mail server. In most cases there's no need to tweak any compiler-specific settings. Note that there currently may be some unresolved issues with gcc 2.96. gcc 2.91 has been tested and known to work. Occasionally some of your system libraries may be stuck in some oddball directory that is not searched by default. Non-standard options for the compiler or linker can be set by putting them into environment variables. This must be done before running the configurescript:

The complete reference to all configure script options is provided below. The most important options are:

configure reference

Here's a comprehensive list of options for the configure script. They are presented in no particular order. In almost all cases, the configure script will automatically figure out the correct values, but sometimes it is necessary to specify them explicitly. If you ever have a need to manually specify any configuration option, try to determine whether you need it because of a particular unique case that involves your server only, or whether it affects any server running your hardware, or system. In the later case, try to investigate if it's possible for configure to be a bit smarter and make the right decision.

IPv6

IPv6 support in the Courier mail server means basically the following:

IPv6 implementations are required to accept IPv4 connections on IPv6 sockets, so IPv6 sockets should be able to receive both IPv4 and IPv6 connections. In the event that your IPv6 implementation is not stable, or is partially incomplete, IPv6 support in the Courier mail server should be disabled.

The configuration script will attempt to detect whether IPv6 structures and functions are available, and automatically enable IPv6 support if they are found. The --without-ipv6 option disables IPv6 support, which may be desired for the following reasons:

IPv6 support is still a bit spotty in some places. If the configuration checks fail, IPv6 support will be quietly suppressed. If you expect IPv6 support to be present, the --with-ipv6 flag can be used to abort configuration if IPv6 support was not detected.

Compile and run make check

    make
    make check

If the configure script ran without errors, run make to build the Courier mail server. If make completes succesfully, run make check. make check runs some simple internal tests. It is not feasible to run a complete check of the Courier mail server's behavior, but make check does automatically run some tests on several modules.

If make check fails, you need to do some detective work. Investigate the source of the failure. It is possible that the issue can be resolved by specifying different options to the configure script, in which case you have to go back and rerun the configure script again.

Installation

su yourself to root, if you want to do a live install, then run make install or make install-strip to install the Courier mail server. If you use the GNU version of make, and you would like to see which files the Courier mail server installs and where, don't su yourself to root, but set the make variable named DESTDIR. For example:

make install DESTDIR=/var/tmp/courier-inst

The contents of DESTDIR are prepended to the name of every file installed, so if --prefix was set to /usr/lib/courier, the files will be installed in /var/tmp/courier-inst/usr/lib/courier. This only works if you use GNU make.

NOTE: you must make sure that your umask is 022 before you run make install.

If executed by root, make install automatically sets the correct ownership on the installed files. Non-root make installs do not set the ownership, but still set correct permissions. This feature is mainly for use by people who are rolling the Courier mail server into a prebuilt package, since this allows them to build the package as a normal user, not root. In this situation the command make install-perms will be very useful. This command creates a file called permissions.dat. This file contains a complete listing of everything that will be installed, and what the correct permissions are on every file.

make install installs the Courier mail server binaries with debugging data, which is probably a good idea to do while the Courier mail server is in development. Use makeinstall-strip to install binaries without debugging data. Some systems have a broken install utility, so make install-strip may fail.

Install configuration files

The following command creates and updates configuration files. It must be executed after running make install:

make install-configure

This command copies each configuration file "filename.dist" to "filename". The existing filename is backed up as filename.bak. If upgrading from the Courier mail server 0.30 or later, the previous configuration settings in filename.bak will be automatically copied to filename, provided that they are still valid. If a configuration setting may no longer be valid, it will be reset to its default value. The output of make install-configure will indicate the status of each configuration setting, therefore it is advistable to save the output to a file, and examine it:

make install-configure >upgrade.log

Versions prior to 0.30 cannot have their configuration settings automatically preserved, and must be restored manually from filename.bak. Do not simply copy filename.bak to filename, this will lose all the formatting codes that allow automatic upgrades.

PAM configuration

If you use PAM library for authentication, you may need to set up PAM for authenticating POP3 logins, IMAP logins, webmail logins, and/or ESMTP authentication. In most cases, all you have to do is install /usr/lib/courier/etc/pop3d.authpam as /etc/pam.d/pop3, /usr/lib/courier/etc/imapd.authpam as /etc/pam.d/imap, /usr/lib/courier/etc/webmail.authpam as /etc/pam.d/webmail, and /usr/lib/courier/etc/esmtp.authpam as /etc/pam.d/esmtp. However you will have to consult your PAM documentation, and the manual pages for authpam, in order to make sure.

Some versions of the PAM library, do not use the /etc/pam.d directory. Instead they use a single configuration file /etc/pam.conf. Here's an example of what needs to be added to /etc/pam.conf on FreeBSD 4.0. NOTE: other platforms may need something similar:

imap  auth    required        pam_unix.so      try_first_pass
imap  account required        pam_unix.so
imap  session required        pam_permit.so
pop3  auth    required        pam_unix.so      try_first_pass
pop3  account required        pam_unix.so
pop3  session required        pam_permit.so
esmtp auth    required        pam_unix.so      try_first_pass
esmtp account required        pam_unix.so
esmtp session required        pam_permit.so

Building RPM and DEB packages

NOTE: If an RPM or a DEB package gets built as per this INSTALL file resulting packages may not install if you have an existing IMAP or an existing POP3 server installed. The RPM packages will contain these PAM configuration files, and they will conflict with any PAM configuration files installed by another IMAP or POP3 server. If you manually installed an IMAP or a POP3 server without creating a distribution package, the Courier mail server package will install and the old configuration files will get silently removed, since they were not installed using rpm or dpkg.

The Courier mail server includes integrated POP3, IMAP, and webmail servers, however they only work with maildirs. Decide if you want to keep using your current server, or switch to the Courier mail server's IMAP/POP3/webmail servers. If you want to keep your existing servers, back up the contents of your /etc/pam.d directory before installing the RPM or the DEB package, install it, then restore the overwritten files. If you want to switch to the Courier mail server, blow away your current server before running make install.

Adjust system paranoia level

There are four setuid binaries in the Courier mail server that are owned by root: sendmail, maildrop, webmail and webadmin. There's also one setgid binary, sqwebpasswd.

/usr/lib/courier/bin/maildrop is the mail filter. If you do not need mail filtering, you can remove it. The setuid root privilege is only needed to implement mail filtering "on the wire", when receiving mail from an external mail relay (see localmailfilter(7) for more information). Removing the setuid root bit still allows traditional mail filtering to be used, after the message is received and delivered to the mailbox.

/usr/lib/courier/libexec/courier/webmail/webmail is the webmail CGI. It is executed by the web server, and needs to change its userid/groupid, in order to enter the maildir. If you do not need webmail access, you can remove it. An alternative is to implement virtual mailboxes, owned by a non-privileged userid, and change the ownership of the webmail CGI to the non-privileged user (you will also need to use the --with-cacheowner option to the configure script since the webmail process must have write access to the webmail login cache directory).

/usr/lib/courier/libexec/courier/webmail/webadmin is the wrapper for the web-based administration tool. See below for more information.

/usr/lib/courier/bin/sendmail is the command line mail sender. Its first order of business is to set its group id to the Courier mail server's group id, and restore the original userid, dropping root. The reason that it needs root setuid is to set its real group id, because setting the setgid bit on the executable is not enough. The setgid bit sets only the effective group id, and the root setuid bit is required to set both effective and real group ids. Both real and effective group IDs are needed in order to be able to implement maildrop mail filtering.

/usr/lib/courier/libexec/courier/sqwebpasswd is described in detail in the "OPTIONAL: Changing mail account passwords using the webmail server" section.

Post-installation setup

A first-time the Courier mail server installation may not require the system startup scripts to be modified to start the Courier mail server at system boot. Until the system's functionality is verified, the system will probably continue to use the existing mail server. Still, most the Courier mail server configurations will require two things to be started before any part of the system is put to use:

Post-installation checks

The following tests should be run to verify that your installation works properly. These tests are not really comprehensive tests, they only make sure that the basic functionality is there, and they definitely must be done the first time you install a version of the Courier mail server on your system. If you later reinstall the same version on the same platform, using the same configuration, you don't need to run these installation checks (but you better be sure that the reinstallation is COMPLETELY identical to the original install). You might also wish to rerun these installation checks after upgrading your base operating system.

The following documentation assumes that the Courier mail server is installed in /usr/lib/courier.

Verify module installation

Run the showmodules utility after all files have been installed, but before you attempt to start the Courier mail server. The showmodules utility attempts to load and initialize transport modules that have been configured, without actually starting up the Courier mail server. Running showmodules should result in something that looks like this:

   showmodules[5060]: Loading STATIC transport module libraries.
   showmodules[5060]: Installing i586-gnu-linux [0/0]
   showmodules[5060]: Installing local
   showmodules[5060]: Installed local
   showmodules[5060]: Installing esmtp
   showmodules[5060]: Installed esmtp
   showmodules[5060]: Installing dsn
   showmodules[5060]: Installed dsn
   showmodules[5060]: Initializing local
   showmodules[5060]: Initializing esmtp
   showmodules[5060]: Initializing dsn

Test child process termination

In this test, you will start the Courier mail server, then attempt to rapidly pump through as many messages as fast as possible, to verify that asynchronous child process termination handling works. For this test (and the following tests) you need to use a test account.

Log on to the test account and run maildirmake to create two maildirs: maildirmake $HOME/test, and maildirmake $HOME/bounces.

Create $HOME/.courier-test-default, containing one line: ./test. Create $HOME/.courier, containing one line: ./bounces. If you previously selected .qmail compatibility, you will need to use .qmail-test-default and .qmail, of course. Keep that in mind as you work through the remaining tests.

Start the Courier mail server as root:

/usr/lib/courier/sbin/courier start

Check your system log files for any error messages. Run the ps command, and check that you only have the following processes running: courierd (two processes), courierdsn, courieruucp, courieresmtp, and courierlocal. You will also have a couple of "logger" processes hanging around, that's ok too.

One of the two courierd processes will be running as root. The courierlocal process will also be running as root. All other processes will be running as the courier (or daemon, or mail) user. courieruucp may be running as uucp.

Run the perftest1 script, which can be found in the directory containing the Courier mail server's source code:

sh perftest1 1000 "user-test-1 user-test-2 user-test-3 user-test-4 user-test-5"

Run this script while logged on to the test account. Replace "user" with the name of your test account. This will send 1000 messages with five recipients per message. You should end up with exactly 5000 messages in $HOME/test/new. Count them.

Monitor the system logs. There will be a lot of activity. On my test system, the system logger usually backs up. The Courier mail server generates log messages faster than the logger can record them. When all the activity stops, count how many files you have in $HOME/test/new. For extra credit, total up the Delivered-To: headers in all the messages, there should be 1000 headers for each one of the five addresses.

If you did not get 5000 messages, and mailq comes up empty, check $HOME/bounces/new. If you're lucky, the rest bounced. That's still a problem, but the bounces will help you to investigate things further.

If you did not get 5000 messages, and mailq shows some messages remaining in the queue, and ps shows some dead zombie processes that are not being reaped, this means that asynchronous process termination is not working. You will need to examine your configuration to see whether configure selected the wait or the wait3 function. Unpack the source code again and rerun configure. This time use the --with-waitfunc option to choose the other wait function, manually. Recompile, reinstall, and rerun this test.

If you did get all the messages, go through your syslog for extra-extra credit. grep it for the word "defer" to see if any messages required multiple delivery attempts. This shouldn't happen either.

If your hardware has enough juice to pump through 5000 messages in a short period of time, rerun this test with a larger number of messages. Before doing that, wipe the Maildirs clean, in order to confirm the message count, later. The test must run for at least 3-4 minutes in order to get meaningful results.

User/group ID check

For this test you will need to use or create a regular user test account, which will be referred to as user. You can use the same test account you used in the last test, but erase all .courier (or .qmail) files.

In user's home directory, create .courier which contains the following text:

| /usr/bin/id >ID
| /usr/bin/env >ENV

Make sure that your id and env commands are in /usr/bin. If not, use the correct path.

Send a single message to user:

echo "To: user" | /usr/lib/courier/bin/sendmail

Thie message will disappear into the never-never land, so don't waste time looking for it. Just examine, very closely, the contents of the ID and the ENV files in user's home directory. Double check what user and the group ids recorded in ID match user's. Pay close attention to any auxiliary group IDs, make sure that they haven't "leaked" from the root user who started the Courier mail server.

Also, examine the environment, in ENV. Check the manual page for dot-courier, ENV should contain only the documented environment variables, and any environment variables that are defined in the /usr/lib/courier/etc/courierd file.

OPTIONAL: Configure webadmin

This is a web-based administration tool. webadmin is a web CGI application. It is necessary to have a local web server installed in order to use webadmin. Apache will do, but so will any other server with a complete CGI implementation (PHP is not required). Installing webadmin is a three step process:

  1. Move /usr/lib/courier/libexec/courier/webmail/webadmin to your web server's SSL cgi-bin directory.

  2. Add the following command to your system startup script:

    /var/www/cgi-bin/webadmin daemon &

    (or the actual cgi-bin directory). Executing the cgi-bin webadmin with a "daemon" parameter starts the daemon process.

    It might be useful to manage webadmin with courierlogger: using "courierlogger -pid=/usr/lib/courier/var/webadmin.pid -start .../webadmin daemon" to start webadmin and "courierlogger -pid=/usr/lib/courier/var/webadmin.pid -stop" to stop it.

  3. Execute "make install-webadmin-password". This prompts for a password, which is saved in the file /usr/lib/courier/etc/webadmin/password.

  4. Edit "/usr/lib/courier/etc/webadmin/restartcmd", this file contains one line, a command that webadmin runs to restart courier. This defaults to "courier restart". If Courier gets set up to run under systemd this should be changed to like:

    systemctl restart courier.service &

    ... or try-restart. It is important to use & to run systemctl in the background. webadmin uses this as an indication for proper signal handling setup. webadmin blocks signals when installing an updated configuration, but commands executed in the background have their signal handling reset to default. systemd will signal processes to terminate when restarting them. webadmin's blocked signals permit it to finish installing any remaining updates. systemctl will wait for the restart to finish, but it's part of the service that's getting restarted, so this process needs to run in a background, with default signal handling so that systemctl itself gets terminated.

  5. Edit "/usr/lib/courier/etc/webadmin/restartauthcmd", this file contains one line, a command that webadmin runs to restart the Courier authentication library service. This defaults to "authdaemond restart". If courier-authlib gets set up to run under systemd this should be changed to an "systemctl restart", or maybe "systemctl try-restart", for example: systemctl try-restart courier-authlib.service.

  6. The web server SHOULD be configured to run webadmin from the cgi-bin directory using SSL only. webadmin's authentication is rather simple: the password is saved in a cookie. Unless SSL is used, the webadmin password can be intercepted in transit. If SSL is not available, an acceptable level of security can be achieved by setting up a firewall that allows web access only from trusted IP addresses, then use a dedicated webadmin password. This is not perfect, but is generally adequate. A firewall is a good idea even if SSL is used. This is not Fort Knox, and webadmin is not going to be publicly accessible, so the only needed security is to keep everyone out except for authorized IP addresses.

    Note that webadmin, by default, will enforce this restriction: either SSL, or access from a local IP address. Create an empty file /usr/lib/courier/etc/webadmin/unsecureok to allow non-SSL webadmin connections from remote IP addresses. Alternative, the unsecuredok file may consist of a single line with one or more IP addresses, separated by spaces. Non-SSL access will get accepted from these IP addresses only:

    echo 192.168.0.9 192.168.0.10 >unsecuredok

webadmin is designed to be self-explanatory. Configuration options are divided into logical sections. Changes made to configuration options do not take effect immediately. To apply configuration changes, select "Install new configuration" from the main menu. To cancel all changes made, select "Cancel new configuration". Selecting "Install new configuration" will apply all the changes to the configuration files, and restart any the Courier mail server modules that must be restarted in order for the changes to take effect.

If you decide to use webadmin, most of the remaining steps in this INSTALL document can be done using webadmin's equivalent screens.

Create system aliases

You must now specify which account gets postmaster mail. The Courier mail server does NOT deliver any mail to root. You must use a non-privileged for postmaster mail. You will also need to specify where your postmaster account is. In the following example the same account is used for both, but you can easily use separate mailboxes.

Let's say that you want postmaster mail to be delivered to the user "admin".

Create /usr/lib/courier/etc/aliases/system using any text editor. An example aliases/system file is created by make install, and you can simply edit what you have there. The default contents of this file are as follows:

root: postmaster

mailer-daemon: postmaster

MAILER-DAEMON: postmaster

uucp: postmaster

You need to append the following line:

postmaster: admin

These aliases cause all mail addressed to root, postmaster, or mailer-daemon, to be delivered to admin's account. If you want root's mail delivered somewhere else, you can replace "root: postmaster", with something else.

Run the following command as root:

/usr/lib/courier/sbin/makealiases

This command creates /usr/lib/courier/etc/aliases.dat, a database that contains your new aliases.

Send a test message:

echo "To: postmaster" | /usr/lib/courier/bin/sendmail

Check admin's mailbox, the message should be there.

Let's do it again:

echo "To: postmaster" | /usr/lib/courier/bin/sendmail -Nsuccess

This time, in addition to the blank message, the sending account should receive a return receipt.

Additional aliases can be either added to this file, or placed in any other text file in the /usr/lib/courier/etc/aliases directory.

Create smtp access list

You need to define which IP addresses are allowed to relay SMTP mail through the server. The installation script creates /usr/lib/courier/etc/smtpaccess/default containing an example of how to enable relaying for IP address 127.0.0.1, and several reserved netblocks. You can either append additional entries to this file, or put your additional entries in any other file in the /usr/lib/courier/etc/smtpaccess subdirectory. Afterwars, run the following as root:

/usr/lib/courier/sbin/makesmtpaccess

This command creates the /usr/lib/courier/etc/smtpaccess.dat database that couriertcpd uses to initialize the environment for courieresmtpd.

You will need to rerun makesmtpaccess in order to rebuild smtpaccess.dat after any changes in the smtpaccess subdirectory.

The default the Courier mail server configuration applies smtpaccess.dat to both the regular ESMTP server (port 25), and the message submission server (port 587). It is possible to set up different access files for both ports. To do that, edit /usr/lib/courier/etc/esmtpd-msa, and explicitly set ACCESSFILE to a different file, create that file, and use the makesmtpaccess-msa command to compile the dedicated port 587 access database.

NOTE: Authenticated SMTP is preferred over defining explicit IP address ranges. When combined with SSL, authenticated SMTP enables relaying privileges to any sender that securely provides a valid login/password, from any IP address, instead of only a small range of preauthorized IP addresses. The "OPTIONAL: Configure ESMTP authentication and SSL" section, later in this installation guide, gives more information on enabling authenticated SMTP and SSL-based encryption.

Furthermore, preauthorized IP address ranges are vulnerable to being a source of abusive backscatter E-mail. Using authenticated SMTP together with the optional backscatter setting, described in the following section, prevents transmission of abusive backscatter bounces to external recipients even from trusted senders that have been compromised.

Backscatter suppression

NOTE: It is important to know that the Courier mail server's default backscatter configuration means that if the Courier mail server receives a message for delivery to a local mailbox, and encounters an error during the delivery, the sender may not receive a delivery failure notification. The most common reason is an error in a custom mail filtering script. The next most common reason is a configuration error (the Courier mail server authentication library gives the account's home directory, optional non-default mailbox location, the account's system userid and groupid; but they differ from the actual files and directories (the home directory or the account's mailbox does not exist, exists somewhere else, or they're owned by a different userid or groupid).

When installing the Courier mail server for the first time, it is usually helpful to termporary turn off the default backscatter filters, by setting BOFHSUPPRESSBACKSCATTER to "none", as described below. Remove this setting after the Courier mail server is installed and its basic functions appear to be working.

The term "backscatter" refers to non-delivery reports sent to a forged return address. SMTP was created a long time ago, in better times when everyone trusted each other. Anyone could provide any return address for any E-mail message.

Times have changed. At the time this documentation is written, most surveys report that between 75% and 80% of Internet E-mail is junk E-mail or viruses, with a forged return address.

Backscatter becomes a problem when a mail server does not reject unwanted mail. The mail server decides that the message is unwanted only after it is accepted. It generates a non-delivery notice, and sends it to the original message's return address. Because viruses and junk mail use random forged return addresses, the unfortunate victim of address forgery must deal with large amounts of useless non-delivery notices from the mailbox. Not to mention a bunch of uninformed people who think he is responsible for sending the virus or the junk mail to them.

There's now a growing consensus that backscatter bounces should be considered E-mail abuse. The Courier mail server is already very good at minimizing the amount of backscatter, by the virtue of refusing to receive any mail to a nonexistent local mailbox. However it's still possible for the Courier mail server to bounce a received message. Several settings control how the Courier mail server filters out its own backscatter, and avoids becoming a nuisance to others.

Two settings are available. The first setting instructs the Courier mail server to simply discard backscatter bounces. This is the ESMTP_BLOCKBACKSCATTER setting in the courierd configuration file. This setting lists the so-called "message sources" which are dropped by the SMTP client. All messages from any matching source are quietly discarded. The default setting lists one message source: a code that means "a delivery status notification for a message received via SMTP from a non-authenticated source". "Non-authenticated" means a message received from an IP address that does not have relaying privileges, and did not authenticate. It's also possible to include authenticated SMTP sources; or it's possible to disable this setting altogether, instructing the Courier mail server to deliver all bounces via SMTP, even if they may potentially be backscatter.

Note that messages received in other ways (such as messages sent via the sendmail command) are not affected. Their bounces will be sent via SMTP in all cases (although there exists an undocumented setting to block those bounces too). Also, bounces are always delivered to local mailboxes, this setting is ignored for local mail deliveries.

The default setting means that if the Courier mail server receives a message via SMTP for delivery to a local mailbox, and it bounces for some reason, the bounce will be discarded.

The Courier mail server is also often used as a smarthost for SMTP clients. These SMTP clients either connect from trusted IP addresses (IP addresses that belong to the organization that runs the mail server), or that succesfully authenticate, using SMTP authenticate. If those messages bounce, the non-delivery report gets delivered, because the default setting only drops bounces from non-authenticated source (a connection from a trusted IP address is always processed as if the sender succesfully authenticated).

NOTE: Sometimes the Courier mail server serves as a backup MX for another organization. If mail cannot be delivered to the primary MX (it rejects the message, or the message times out), the bounce will be discarded, because the message was probably received from a non-authenticated source.

The second setting minimizes the possibility of generating a bounce, of any kind, in the first place. The second setting controls the backscatter suppression list, which is a list of blacklisted E-mail addresses.

When the Courier mail server fails to deliver a message to an address, this address goes on the suppression list, and the Courier mail server will refuse to accept any more messages to the same address. If the delivery failure was a temporary failure, any future messages will also be turned away with a temporary error. A permanent delivery failure results in future messages rejected with a permanent error.

Note that the suppression list does not apply to messages already accepted by the Courier mail server, and which are in its mail queue. The suppression list is checked when the Courier mail server is receiving a new message. The Courier mail server automatically clears an address from the suppression list after two hours. If the original message encountered a temporary delivery failure, The Courier mail server periodically tries again to re-deliver the message. If the message continues to encounter a temporary delivery failure, the clock starts running again, from the beginning, If a re-delivery attempts succeeds, the address is cleared from the suppression list, and the Courier mail server will now accept more messages to the same address, immediately.

If a message keeps encountering temporary delivery failures, the time before re-delivery attempts gets longer. It's possible that it could take more than two hours for another delivery attempt, on a busy mail server. The address then falls off the list, and the Courier mail server will accept another message to the undeliverable address. This situation is unavoidable, but is not considered to be a major issue.

The second setting is the BOFHSUPPRESSBACKSCATTER setting, in the bofh configuration file. See the courier(8) man page for more information. The default BOFHSUPPRESSBACKSCATTER setting also filters only messages from non-authenticated SMTP sources against the suppression list.

The suppression list is not updated when problematic messages are manually removed from the mail queue (using the "courier cancel" command). Even though the stuck messages are deleted, The Courier mail server will continue to refuse messages to suppressed addresses, until they time out. Use the "courier clear" command to manually clear addresses from the suppression list, if so desired.

NOTE: A mailbox that exceeded its storage quota results in temporary delivery failures. Therefore, when a mailbox fills up, The Courier mail server stops accepting any more messages to this mailbox (there might be one or two messages already in the mail queue, but that shouldn't be a major issue). Mail deliveries will resume when the mailbox goes below the quota (although this may take an hour, or two, as explained previously). It's possible that an existing version of the Courier mail server was originally modified to generate a permanent delivery failure for a quota exceeded condition. This change should now be undone, in order for backscatter suppression to work properly.

The third setting is the DSNTOAUTHADDR=1 setting in the courierd configuration file. This setting, when enabled, alters bounce handling of messages that were received from an authenticated SMTP connection.

Bounces of authenticated messages are processed according to the previous two settings, except that the bounce message gets sent (if it gets sent at all) to the authenticated login address, instead of the message's return address.

NOTE: This works only if the Courier mail server is configured, via the Courier mail server Authentication Library, to validate login IDs that consist of a full E-mail address, "user@domain", with the login ID corresponding to the mailbox's E-mail address.

Enabling this setting removes the possibility of the Courier mail server sending abusive backscatter bounces to external recipients, from a compromised trusted sender, even if the compromised trusted sender uses authenticated SMTP. Instead of sending the bounces to the forged return address, they get redirected to the sender's mailbox.

NOTE: The authenticated address is used for bounces only. When the message gets sent to its listed recipients, the message's return address gets used, as usual.

NOTE: Authenticated SMTP must be used for this option to have any effect. When relaying privileges are granted to explicit IP address ranges (see the preceding "Create smtp access list" section), The Courier mail server will not have the sender's authenticated login address (unless the sender voluntary authenticates).

Miscellaneous configuration

Review/edit contents of various configuration files in /usr/lib/courier/etc:

Qmail compatibility mode.

echo "qmail" >/usr/lib/courier/etc/dotextension

Run this command if you are installing the Courier mail server on a system that's currently running the Qmail mail server. The Courier mail server will now read .qmail files for delivery instructions, instead of .courier files. The Courier mail server's .courier files are mostly compatible with Qmail's .qmail files, but there are some minor differences. Still, most of your .qmail files should work without too many problems.

Define local domains

The configuration file /usr/lib/courier/etc/locals is a list of all the domains that are considered local. Mail to any address in any local domain is handled as a local delivery. If this file does not exist the Courier mail server will use the contents of the me configuration file, or it will obtain its machine name from the operating system.

This file contains a list of domains, one per line. In most cases you need to initialize this file to contain every hostname that has a DNS A, or AAAA, record pointing to any IP address assigned to this machine, including "localhost". You will also need to include any domain that lists this machine as its primary MX relay.

You may also include domain wildcards in locals by prefixing the domain with a period. For example: ".example.com" will treat any domain underneath example.com - like a.example.com, b.example.com - as a local domain. Note that this does not include example.com itself, so you may need to list it explicitly as well!

NOTE: The makealiases command must be entered after making any changes to this file.

Create a list of domains to accept mail for

If you would like your server to function as a backup mail relay for other domains, create /usr/lib/courier/etc/esmtpacceptmailfor. This is a plain text file, containing a list of domains, one per line. This file lists all domains your server will accept mail for. NOTE: if you create this file, you MUST include all your local domains. Usually you can simply append what you have in /usr/lib/courier/etc/locals. If /usr/lib/courier/etc/esmtpacceptmailfor does not exist, The Courier mail server will accept mail only for the machine name listed in /usr/lib/courier/etc/me, (or the system machine name).

Like /usr/lib/courier/etc/locals, prepending a period to a domain name in esmtpacceptmailfor will cause the Courier mail server to accept mail for all subdomains of this domain.

OPTIONAL: Configure UUCP

The Courier mail server is capable of sending and receiving mail via UUCP. The Courier mail server does not implement UUCP directly, but instead uses your existing UUCP software to send and receive mail.

The Courier mail server's UUCP functionality has been tested with Taylor UUCP 1.06. It's likely that some minor tweaking will be necessary to get the Courier mail server working with other UUCP builds. Give it a shot, and keep an eye out for problems.

/usr/lib/courier/etc/uucpme

This configuration file must be initialized to list the UUCP node name that this machine is known as. Currently the Courier mail server does not support multiple UUCP node aliases for the same machine.

/usr/lib/courier/etc/uucpneighbors

This configuration file contains a list of all the nodes that your machine talks to via UUCP. Obviously this information will be a duplicate of the corresponding data in your existing UUCP configuration files, and some maintenance will be necessary to keep both lists in sync. That is, unfortunately, unavoidable. The makeuucpneighbors commands turns this plain text file into a database, which is what the Courier mail server uses directly. The format of the uucpneighbors configuration file is described in the makeuucpneighbors(8) manual page.

/usr/lib/courier/etc/uuucprewriteheaders

The Courier mail server automatically rewrites message envelope addresses from ESMTP to UUCP format. If this file exists, the addresses in the headers of messages sent to/from UUCP addresses will also be rewritten.

Configure UUCP domain aliases

The Courier mail server can accept mail addressed to <user@example.com>, and then forward it to uucp!bang!path!user, via UUCP. This is done by adding a UUCP virtual domain alias to your aliases file, see "Create system aliases". Append the following entry to your /etc/aliases, then run the makealiases command:

   @example.com: uucp!bang!path!

See the makealiases(8) manual page for more information.

OPTIONAL: Configure LDAP aliasing

In addition to using LDAP for authentication and for managing accounts, The Courier mail server can use an LDAP directory for routing, or "aliasing" mail.

The term "aliasing" refers to substituting one or more addresses for another address. A one-to-one substitution results in the Courier mail server accepting mail for one address, and delivering the mail to another address. A one-to-many substitution results in the Courier mail server accepting mail for one address, and delivering a separate copy of the message to every address defined by the alias.

The Courier mail server supports a basic form of aliasing using a GDBM or DB-based database. The makealiases(8) command reads a plain text file containing the aliasing rules, the creates a GDBM or a DB database. Each recipient address is looked up in the database, and if an alias is defined for the recipient address, it is used in place of the original address. Aliasing can be used against individual addresses, one by one. An extended form of aliasing maps an entire domain to a single local address, using dot-courier(5) delivery instruction files.

The Courier mail server can use an LDAP directory instead of a GDBM or a DB database, to perform essentially the same function. If OpenLDAP is available at time of installation, the installation script installs the courierldapaliasd(8) program and a ldapaliasrc configuration file. It will be necessary to enter appropriate information into ldapaliasrc, and arrange to run "courierldapaliasd start" at system boot time (it is a background daemon process that opens persistent connections to the LDAP server).

Additional instructions for setting up LDAP-based aliasing are found in the courierldapaliasd(8) manual page.

OPTIONAL: Enable standard mail filters

The Courier mail server includes several options for selectively filtering mail. In general, The Courier mail server provides several plug-in interfaces for external mail filters, that can be used to selectively accept or reject messages.

Please note that running mail filters can have a non-trivial impact on mail system performance and throughput.

There are three standard mail filtering modules:

To enable a mail filter, for example:

filterctl start verifyfilter

The filterctl installs the filter, and the courierfilter starts them, see Starting and stopping the Courier mail server.

OPTIONAL: Configure custom mail filtering

The Courier mail server comes with some sample code that demonstrates how to write a mail filter. The Courier mail server provides two mail filtering interfaces:

See courierfilter(8) for more information on global mail filters.

See maildropfilter(7) for more information on local mail filters.

Miscellaneous UUCP configuration

The Courier mail server sends UUCP mail by running rmail via uux. The configuration script searches for the uux command in the default search path. If your uux command is not in a directory that's in your search path you will have to modify PATH before running configure.

The Courier mail server receives UUCP mail by expecting your UUCP software to run the rmail command, which is installed in /usr/lib/courier/bin. (It's actually a soft link to sendmail, but we'll talk about it later). Your UUCP software probably does not run commands from this directory by default, so you will have to make the necessary adjustments. You can always create another soft link in a directory that UUCP searches by default.

Starting and stopping the Courier mail server

To start the Courier mail server, run the command /usr/lib/courier/sbin/courier start. To stop the Courier mail server, run the command /usr/lib/courier/sbin/courier stop. See the courier(8) manual page for more information.

You should add these commands to your system startup and shutdown scripts.

Note that this command starts and stops the Courier mail server's core processes only. It does not start any additional daemon processes that you may need, such as the mail filtering daemon, the ESMTP server daemon, the POP3 server daemon, or the IMAP server daemon.

The commands courierfilter start, courierfilter stop, esmtpd start, esmtpd stop, esmtpd-msa start, esmtpd-msa stop, pop3d start, pop3d stop, imapd start, and imapd stop (all commands are installed in the sbin directory) are used to start or stop their respective daemons, and they should be added to your system startup and shutdown scripts, where required. As described in the relevant manual pages, courierfilter should be the first daemon process to start, and the last one to terminate. The remaining daemons may be started in any order.

Run the Courier mail server in parallel to your mail server

You now have several options for migrating from your existing mail server to the Courier mail server:

OPTIONAL: Configure ESMTP authentication and SSL

The Courier mail server supports authenticated ESMTP in order to grant ESMTP relaying privileges to remote users. The following steps set up authenticated ESMTP:

ESMTP over TLS/SSL

The Courier mail server also supports ESMTP over TLS/SSL, by using the ESMTP STARTTLS extension:

The Courier mail server will also use TLS/SSL when sending ESMTP mail, automatically. If the remote mail server support STARTTLS, The Courier mail server will use it automatically.

SSL/TLS settings for the ESMTP client can be adjusted in the /usr/lib/courier/etc/courierd configuration file. When sending mail using SSL, The Courier mail server can optionally verify the remote server's X.509 certificate. This is done by setting ESMTP_TLS_VERIFY_DOMAIN to 1, in /usr/lib/courier/etc/courierd.

The configuration script checks for the system's list of trusted certificate authorities, and initializes TLS_TRUSTCERTS in the courierd configuration file, during installation. When the Courier connects to a remote server, setting ESMTP_TLS_VERIFY_DOMAIN to 1 in the courierd configuration file (usually /usr/lib/courier/etc/courierd or /etc/courierd) enables certificate verifications. However, many mail servers on the Internet use self-signed certificates, so this is generally of little use.

OPTIONAL: Configure ESMTP smarthosting

Initialize the esmtproutes configuration file if all outgoing mail need to be forwarded to your Internet provider's mail server, or some other "smarthost". See courier(8) for more information:

: relay.example.com

This forwards all mail to relay.example.com

: relay.example.com,587

This forwards all mail to relay.example.com on port 587.

: relay.example.com,465 /SECURITY=SMTPS

This forwards all mail to relay.example.com on port 465, using encrypted SMTP.

If the smarthost requires authentication, initialize the esmtpauthclient configuration file:

relay.example.com,587 john@example.com snerkle

When the Courier mail server connects to relay.example.com on port 587, it will authentication using the userid of "john@example.com" and password "snerkle".

OPTIONAL: Configure the SECURITY ESMTP extension

The Courier mail server includes an experimental extension to ESMTP that can be used to set up secure E-mail delivery between trusted mail relays over an untrusted network. This is implemented by an experimental ESMTP extension in the Courier mail server. Therefore, at present time both the sending and the receiving mail relay must be running the Courier mail server that's configured to support this extension. The specification for this ESMTP extension is publicly available. This is a very small extension of the existing, draft-standard STARTTLS ESMTP extension. The SECURITY extension should only require minor changes to existing mail servers and clients that already implement STARTTLS.

Overview

The first necessary step is to read the formal definition of the SECURITY extension, which can be found on https://www.courier-mta.org. Although the following instructions do not use any information directly from this document, it is important to understandi how this mechanism works. This will be very useful in troubleshooting. This is not called an "experimental" extension just for the hell of it.

The SECURITY extension builds on top of several existing, proven, technologies in order to deliver mail with the highest level of security that can possibly be implemented using the existing technology. The several steps in implementing the SECURITY extension:

  1. Install and configure the STARTTLS ESMTP extension. This extension uses TLS/SSL encryption for sending mail.
  2. Create a private, controlled, X.509 Certificate Authority.
  3. Use the private CA to sign X.509 certificates of all mail nodes in the trusted mail network. This CA's certificate is also installed in every trusted mail node.

The SECURITY extension is an optional tag that's attached to an E-mail message. The Courier mail server requires STARTTLS to forward SECURITY-tagged messages, and the receiving mail nodes must present an X.509 certificate, signed by the private Certificate Authority, before the Courier mail server will send the message. The Courier mail server will refuse to send the message to a mail node that does not support STARTTLS, or doesn't present a suitable X.509 certificate.

Therefore, in an ideal world, mail clients will simply tag messages with the SECURITY extension. Obviously, this means that mail clients must be updated to implement this feature. Until this happens, The Courier mail server will provide a workaround that automatically tags all messages for selected domains with the SECURITY extension. This is not a perfect solution, and it has some minor limitations, which will be mentioned later.

Install and configure the STARTTLS ESMTP extension

The first step is to implement ESMTP STARTTLS. Use the instructions elsewhere in this document to activate ESMTP STARTTLS support. The following instructions use the scripts from OpenSSL 0.9.6, but should also work with OpenSSL 0.9.5a.

Create a private X.509 Certificate Authority

Create an empty subdirectory:

    mkdir /etc/myca
    cd /etc/myca

There's a convenient OpenSSL script called CA.pl that you want to copy to the current directory:

    cp /usr/share/ssl/misc/CA.pl .

Your OpenSSL package may have CA.pl installed someplace else. Find it, and copy it to /etc/myca. The CA.pl needs to be slightly modified before it can be used. Find the following commands in CA.pl, and change them as follows:

Replace:

      system ("$REQ -new -keyout newreq.pem -out newreq.pem $DAYS");

replace with:

      system ("$REQ -new -nodes -keyout newreq.pem -out newreq.pem $DAYS");

Also replace:

      system ("$REQ -new -x509 -keyout " .
          "${CATOP}/private/$CAKEY -out ${CATOP}/$CACERT $DAYS");

replace with:

      system ("$REQ -new -nodes -x509 -keyout " .
          "${CATOP}/private/$CAKEY -out ${CATOP}/$CACERT $DAYS");

The CA.pl script creates password-protected certificate keys by default. Password protected certificates currently do not work with the Courier mail server. Adding the -nodes parameter turns off password protection. This means that it is vital to make sure that the trusted mail relays are properly secured. All the encryption in the world will not be of much use if the mail relays are running a rootable FTP server (for example). Anyway, run CA.pl to create a new certificate authority:

    ./CA.pl -newca

CA.pl prompts for a basic description of the new CA, then creates the certificate and the certificate key. The CA's root certificate is saved in /etc/myca/demoCA/cacert.pem.

Use the private CA to sign X.509 certificates of all trusted mail nodes

This step must be performed to create the X.509 certificates for every mail node in the trusted secure network. First, a certificate request is created:

    ./CA.pl -newreq

CA.pl prompts for a basic description of the new certificate. Special care must be paid to the "commonName" setting. "commonName" MUST be set to the hostname of the trusted mail node, NOT its mail domain. For example, given the following DNS setup for example.com:

     example.com.  MX 10 mx1.example.com.
     example.com.  MX 20 mx2.example.com.

     mx1.example.com. A 192.68.0.1
     mx2.example.com. A 192.68.1.1

This domain will need two certificates, one with "commonName" set to "mx1.example.com", and one with "commonName" set to mx2.example.com.

Running ./CA.pl produces a certificate request in the file newreq.pem. Run the following command to sign it:

    ./CA.pl -signreq

This step creates the file newcert.pem that contains a new signed certificate. The private key from the original certificate request must be appended to this file, before the certificate can be used. Simply take the newreq.pem file from the previous step, and append the private key in that file to newcert.pem. The resulting certificate file should look something like this:

   [ description of the certificate ]

-----BEGIN CERTIFICATE-----

   [ binary goo ]

-----END CERTIFICATE-----
-----BEGIN RSA PRIVATE KEY-----

   [ binary goo ]

-----END RSA PRIVATE KEY-----

The OpenSSL documentation contains instructions on how to perform the equivalent procedure with Diffie-Hellman instead of RSA.

Configure trusted mail nodes

Two files must be installed on every trusted mail node.

Edit the /usr/lib/courier/etc/esmtpd configuration file. Set TLS_CERTFILE to /etc/mycert.pem. The Courier mail server will use TLS_CERTFILE to authenticate itself to other trusted mail nodes.

Edit the /usr/lib/courier/etc/courierd configuration file. Set TLS_TRUSTSECURITYCERTS to /etc/cacert.pem. The Courier mail server will not send ESMTP mail tagged with the SECURITY extension to other mail relays unless they produce a certificate that's signed by TLS_TRUSTSECURITYCERTS.

Testing

The following simple steps can be carried out to verify that everything is working correctly. These examples use two mail nodes called send.example.com and receive.example.com. The test messages are sent from send.example.com, and are addressed to receive.example.com. The Courier mail server must be restarted on both send and receive, after reconfiguring the machines for each test. It is not strictly necessary to do this every time, actually, but it's simply easier to do make it a part of the routine. It is necessary to restart both the main the Courier mail server daemon processes as well as the separate ESMTP daemon process (on receive):

    courier stop
    courier start
    esmtpd stop
    esmtpd start
  1. Temporary get rid of /usr/lib/courier/bin/couriertls wrapper on receive.example.com. Rename it to couriertls.save. STARTTLS is automatically disabled if couriertls is missing,
  2. Run the following command on send.example.com: 
        echo "To: postmaster" | /usr/lib/courier/bin/sendmail \
              -S STARTTLS postmaster@receive.example.com

    This message should bounce back since receive has STARTTLS disabled.

  3. Restore couriertls on receive.example.com, but then rename it on send.example.com. The situation is now reversed, and the test message should still bounce.
  4. Restore couriertls on send.example.com. Edit receive's /usr/lib/courier/etc/esmtpd file. Comment out the current TLS_CERTFILE setting (which points to the private CA certificate). Reset TLS_CERTFILE to /usr/lib/courier/share/esmtpd.pem, which is the self-signed test certificate created by the mkesmtpdcert script, when STARTTLS support in the Courier mail server was first set up.

    Send a test message WITHOUT the "-S STARTTLS" option. This message should go through, assuming all the other setting in all configuration files are the initial defaults. The regular ESMTP STARTTLS extension, without authentication, will be used the deliver this message. Verify this by checking the headers in the received message on receive.example.com.

    Send a test message WITH the "-S STARTTLS" option. It should bounce, even though receive.example.com supports STARTTLS. That's because it is using an X.509 certificate that's not signed by the private CA authority.

  5. Restore TLS_CERTFILE on receive, and send a test message with the -S STARTTLS option, which should now go through.

Force SECURITY for selected domains

As demonstrated by the test messages, messages must be tagged with the SECURITY extension in order for them to be securely transmitted. This must be done by the sending mail client. Until mail clients support SECURITY The Courier mail server can automatically add the SECURITY tag to every message addressed to a domain. This is done by entering the domain in the esmtproutes configuration file using the following syntax:

receive.example.com:  /SECURITY=STARTTLS

Repeat the tests in the previous section, but this time add and delete this entry in /usr/lib/courier/etc/esmtproutes instead of using the -S STARTTLS option. The test messages must still bounce or not bounce in the same way.

Consult the courier(8) manual page for more information on the esmtproutes configuration file.

Limitations

This setup makes it virtually impossible to intercept mail traffic between trusted mail nodes. Even if the DNS cache is poisoned to intercept mail to a hostile mail node, mail will not go through since the attacker will not have a signed X.509 cert. However, all is lost if the mail nodes themselves are compromised directly. After securing the compromised node, everything must be rebuilt. A new CA must be created, and all mail nodes must now receive new certificates. Once support for certificate revocation lists is improved, this situation will get somewhat better.

Another possible way to mitigate that possibility is to use a different certificate authority for every trusted mail node. TLS_TRUSTSECURITYCERTS can point to a directory, instead of a file. This directory can contain multiple certificate authorities (hashed by OpenSSL's c_rehash script). Then, only the compromised mail node's authority certificate needs to be tossed out, regenerated, and redistributed.

TODO: it may be possible to avoid generating individual certificates, and distribute self-signed certificate authority certs only, with a properly-initialized commonName field. This needs to be researched.

There are some minor differences between using -S STARTTLS versus putting the domain into esmtproutes. If the sending mail node forward mail to this domain via UUCP, -S STARTTLS will bounce. Since esmtproutes does not apply to UUCP, putting this domain in esmtproutes will have no effect whatsoever.

OPTIONAL: Configure the Sender Policy Framework

The Courier mail server can optionally check the return address on all SMTP mail for the sender's published Sender Policy Framework (SPF). Keep in mind SPF is an experimental protocol that's still maturing. The Courier mail server's SPF configuration is set up in the "bofh" configuration file, and is fully explained in the courier(8) manual page.

OPTIONAL: Configure the IMAP server

The Courier mail server includes an integrated IMAP server. The following steps set it up:

NOTE: if you have previously installed the stand-alone version of the Courier IMAP server, you will need to remove it prior to using the directly integrated version. They use the same base source code, but have a slightly different configuration.

NOTE: this IMAP server supports maildirs only. It does not support mbox file mailboxes.

Configure IMAP shared folders

It is possible to share folders between different mailboxes, via IMAP. See the file maildir/README.sharedfolders.(txt|html) for more information.

OPTIONAL: Configure IMAP over SSL

To add SSL support you have to install OpenSSL or GnuTLS before installing the Courier mail server. Download OpenSSL from http://www.openssl.org/, or GnuTLS from http://www.gnutls.org.

OpenSSL's support is well-tested, the GnuTLS version is a relatively new addition, and is considered experimental. Follow OpenSSL's or GnuTLS's installation instructions, then build the Courier mail server.

NOTE: Most systems already have an available OpenSSL or GnuTLS package. Do not build OpenSSL or GnuTLS yourself, if a prebuilt package is already available. Just install the prebuilt package.

NOTE: The development libraries must be installed in addition to the runtime package, in order to build the Courier mail server. On most systems, the development files (header files, libraries, etc...) are provided in a separate "devel" package. The base OpenSSL/GnuTLS package is not sufficient to build the Courier mail server, the development libraries must be installed.

The OpenSSL library is selected when both OpenSSL and GnuTLS libraries are found by the configure script. Use the --with-gnutls option to explicitly select GnuTLS library over OpenSSL.

The /usr/lib/courier/etc/imapd-ssl configuration file sets some additional options for SSL support, which you may need to adjust. Consult that configuration file for additional information. Then, you also have to run the /usr/lib/courier/sbin/imapd-ssl script from your system startup and shutdown scripts, just like the /usr/lib/courier/sbin/imapd script. You may accept both SSL and non-SSL connections by running both scripts.

Note that SSL requires a valid, signed, X.509 certificate to be installed where the Courier mail server expects to find it. The default location for the X.509 certificate, in PEM format, is /usr/lib/courier/share/imapd.pem. The X.509 certificate must be signed by a certificate authority that is known to the IMAP client. You can generate your own self-signed certificate by running the script /usr/lib/courier/share/mkimapdcert which will work too, except that IMAP clients using SSL will display a warning message the first time they connect to the server. To get rid of the warning message you'll have to pay for a signed X.509 certificate. The gory details of setting up SSL is beyond the scope of this document, and you should consult the OpenSSL documentation for more information.

The mkimapdcert script will not overwrite an existing imapd.pem certificate, in order to allow precompiled packages to simply call mkimapdcert after installation, without worry.

The IMAP server also supports the IMAP STARTTLS extension as an alternative or a complement to IMAP over SSL. The /usr/lib/courier/etc/imapd-ssl configuration file is also used to enable or disable IMAP STARTTLS, which has all the same requirements and prerequisites as IMAP over SSL.

OPTIONAL: Sending mail via an imap connection

This server allows using the IMAP connection to send E-mail. Normally, the IMAP protocol provides only access to mail in an existing mail account, and mail clients must use SMTP in order to send mail. The Courier IMAP server has an optional setting to enable mail to be send via an IMAP connection in a manner that should work with all existing IMAP mail clients. This can be useful when an account is logged in from a shared access pool which normally blocks most access to the SMTP port.

This is implemented by enabling a setting in the imapd configuration file that designates a folder as a special "Outbox" folder. The default setting is a folder called "Outbox" (IMAP path INBOX.Outbox), but the name can be changed to anything. This folder, for the most part, is no different than any other folder. If a folder by that name doesn't exist, it needs to be created, just like any other IMAP folder. It looks and acts like any other folder, except that each message added to the folder, via IMAP's APPEND or COPY command, will also be mailed out by the Courier IMAP server to the addresses listed in the To:, Cc:, and Bcc: headers.

It should be possible to use this to send mail from any IMAP client by:

  1. Composing a draft message, telling the IMAP client to save the draft message in its drafts folder on the IMAP server.
  2. Opening the drafts folder, and moving or copying the message to the Outbox folder.
  3. The act of copying the message into the Outbox folder will send the mail. There won't be any explicit notification to the fact that the message was sent, so it's a good idea to include your own E-mail address on the Cc: list.

NOTE: it is tempting to configure the IMAP mail client to use Outbox as its default folder for saving drafts. Resist the temptation. If you forget, you'll save a partially completed draft, which will be then obediently mailed out.

NOTE: the message, in addition to being sent, will be saved in the folder in the normal fashion. After saving the message, reopen the Outbox folder and delete the sent message, or move it someplace else.

NOTE: when enabled, the Courier IMAP server will advertize a private XCOURIEROUTBOX IMAP capability. It is theoretically possible to code an IMAP mail client that reads this capability and automatically configures itself accordingly -- when this IMAP capability is present -- to send E-mail in the normal way but using the IMAP connection. At this time, I'm not aware of any actual mail clients that know how to do this.

NOTE: many mail clients save some additional internal information in headers of draft messages. The internal information is normally removed before the mail client sends the message. Make sure that none of this extra information is something that should not be mailed out.

OPTIONAL: Configure IMAP realtime folder status updates

It's possible to allow multiple clients to open the same folder, and have all clients to be simultaneously notified of any changes to the folder contents.

After installing the server see the imapd(8) manual page for more information.

OPTIONAL: Configure SMAP

Starting with the Courier mail server 0.43, the IMAP server supports an experimental mail access protocol, dubbed "Simple Mail Access Protocol". SMAP is an experiment to provide enhanced mail processing beyond what's currently possible with IMAP. SMAP's purpose is to prototype and develop advanced mail access functionality that's not possible with IMAP. SMAP is disabled by default. Uncomment the SMAP_CAPABILITY setting in the imapd configuration file in order to enable SMAP. The Cone mail client supports SMAP.

OPTIONAL: Configure the POP3 server

The Courier mail server includes an integrated POP3 server. The following steps will set it up:

NOTE: this POP3 server supports maildirs only. It does not support mbox file mailboxes.

OPTIONAL: Configure POP3 over SSL

Implementing POP3 over SSL is very similar to implementing IMAP over SSL. The only differences are that the startup/shutdown command is "/usr/lib/courier/sbin/pop3d start" and "/usr/lib/courier/sbin/pop3d stop", the configuration file is /usr/lib/courier/etc/pop3d, the name of the required SSL certificate is /usr/lib/courier/share/pop3d.pem, and the command to generate a test SSL certificate is mkpop3dcert.

OPTIONAL: Configure the IMAP/POP3 aggregator proxy

It is possible to distribute IMAP and POP3 mailboxes between multiple server.

See imap/README.proxy for more information.

CERTIFICATE AUTHENTICATION

The Courier mail server can use SSL certificates for authentication purposes. That is, instead of using a login ID and a password, for accessing the mailbox, The Courier mail server uses a client-side SSL certificate. For certificate authentication purposes, one of the fields in your certificates' subject must match the login ID in the authentication database. Consider the following certificate:

...
Subject: C=US,ST=New York,L=New York,O=Acme Widgets Inc,CN=John Smith,emailAddress=johnsmith@example.com

If the emailAddress field is configured as the login ID, the authentication database must provide login details for johnsmith@example.com. To enable certificate authentication, edit the following configuration files in sysconfdir: imapd-ssl, pop3d-ssl, esmtpd and esmtpd-ssl (the esmtpd files enable SSL certificate authentication for incoming SMTP connections, if a good SSL certificate is provided, the client receives mail relaying privileges). All of these configuration files require the same set of changes:

OPTIONAL: Configure the webmail server

The integrated webmail server is made up of two parts. The first part, by default, is installed as /usr/lib/courier/libexec/courier/webmail. You can simply copy this binary executable to your web server's cgi-bin directory, or create a link from the cgi-bin directory to this program. This is a small stub program that connects, via a local socket, to the sqwebmaild daemon process, which implements the webmail service. It is necessary to start the webmail server by adding the following command to the system startup screen (so that the webmail server gets automatically started at boot):

/usr/lib/courier/sbin/webmaild start

(It is also possible to run "webmaild stop" from the system shutdown script in order to shut down webmail service gracefully).

Note that the webmail server is used to access mail in existing accounts only. There is no provision to create accounts through the webmail interface (nor there should be).

SELinux

The following extension may be necessary to make webmail work when SELinux kernel extensions are turned on:

allow httpd_sys_script_t var_t:sock_file write;
allow httpd_sys_script_t unconfined_t:unix_stream_socket connectto;

Spell checking

The webmail server can use either the hunspell, the ispell or the aspell package for spell checking. Install hunspell, ispell or aspell before installing the Courier mail server.

NOTE: Courier mail server assumes that the spell checking dictionary is called "english", for ispell or aspell, and "en_US" for hunspell. Some systems use a different name for the default spell checking dictionary. To change the name of the spell checking dictionary used by the webmail server, put the name of the dictionary into the file /usr/lib/courier/share/sqwebmail/html/en-us/ISPELLDICT.

Images

It is also necessary to install the static icon images used by the webmail server. The installation script copies the static images to the /usr/lib/courier/share/sqwebmail/images directory. By default, the webmail server uses the URL "/webmail/" to specify the location of the static images, for example: /webmail/folders.gif. This means that you must create a subdirectory called "webmail" in your web server's document root - typically /usr/local/etc/apache/htdocs/webmail, or /usr/local/www/htdocs/webmail, or something similar. You will need to determine the actual location of your web root directory, which varies from system to system. Then, create a subdirectory named "webmail", and copy all the icons to that directory.

Another possibility is to install a soft link, instead of creating the webmail sub directory, and point the soft link to /usr/lib/courier/share/sqwebmail/images (you also must make sure that the web server is configured to follow symlinks).

There is a configuration option, --enable-imageurl, that can be used to use something other than /webmail/ as the URL prefix for images.

Alternative timezones

The file /usr/lib/courier/share/sqwebmail/html/en-us/TIMEZONELIST contains a list of alternative timezones. By default all dates and times are shown in the server's default timezone, and the dropdown list on the login screen can be used to select an alternative timezone. The default alternative timezone list that lists only a small number of timezones. Additional timezones can be entered into this file to be shown on the login web page.

LDAP address book import

The webmail server can import E-mail addresses from public LDAP address books into an individual address book. A default systemwide list of accessible LDAP address books is defined for everyone, and individuals can configure additional LDAP address books for themselves.

The OpenLDAP development toolkit must be installed before building SqWebMail, in order for LDAP search code to compile.

The file ldapaddressbook configuration file should contain a default systemwide list of accessible address book. See courier(8) for more information. A default file will be installed, listing some common Internet address books. Each line in this file contains the following information:

name<tab>host<tab>port<tab>suffix<tab>binddn<tab>bindpw

<tab> is a single ASCII TAB character. name is the unique name for this LDAP server. host and port specify the connection parameters. suffix specifies the root LDAP entry whose subtree gets searched. The binddn and bindpw fields are not presently used (they were used in earlier version of the webmail server, before the LDAP search interface was rewritten and simplified).

Webmail session timeouts

A login session is automatically logged out after certain period of inactivity. The timeout period defaults to 20 minutes, and is set by the --enable-softtimeout option to the configure script. It is also possible to adjust this value by setting the SQWEBMAIL_TIMEOUTSOFT environment variable. For example, with Apache, by adding the following to httpd.conf:

SetEnv SQWEBMAIL_TIMEOUTSOFT 3600

There is also a hard timeout, which logs out a session no matter what. The default of two hours is changed with the --enable-hardtimeout option to the configure script, and the SQWEBMAIL_TIMEOUTHARD environment variable.

WARNING:

The hard timeout interval is used to calculate the maintenance of the login cache (if that option is selected). This factor is used in the cleancache.pl cleanup script, and changes to this value must be coordinated appropriately. It is not possible to use different hard timeout values with the same login cache (in different virtual domains, as described in the next session). Leisurely tinkering with this environment variable is STRONGLY DISCOURAGED, it's very easy to screw up the whole system. You've been warned.

If you adjust the hard timeout, you must simultaneously delete your current login cache directory, and adjust $timeouthard in the installed cleancache.pl script.

Maximum message sizes

Messages composed in the webmail server are limited in size. The additional limitation are on top of the limit set in the sizelimit configuration file, see the courier(8) manual page.

The --with-maxargsize, --with-maxformargsize, and --with-maxmsgsize options to the configure script set the parameters that control the maximum size of messages and attachments. These parameters can also be set through the following environment variables.

NOTE: The configure script parameters define the minimum settngs. The following environment variables may be used to set larger limits only.

NOTE: These settings limit only the maximum size of messages sent from the webmail server. The limit on the incoming message size is set by other Courier mail server settings (usually the sizelimit setting also).

SQWEBMAIL_MAXARGSIZE
Approximate maximum size, in bytes, of the message, excluding any attachments (overrides the --with-maxargsize parameter to the configure script). This is the maximum message that can be typed into the webmail server.

NOTE: The webmail server has an inactivity timeout. While composing a new message use the "Preview" button frequently to save the unfinished message and keep the session from timing out.

SQWEBMAIL_MAXATTSIZE
Approximate maximum size, of each allowed attachment. (overrides the --with-maxargsize parameter to the configure script).

NOTE: Attaching binary files to E-mail messages incurs an overhead of approximately 33%. E-mail is really not the optimum medium for exchanging files. Setting SQWEBMAIL_MAXATTSIZE to 4000000 will effectively allow attaching files of up to 3000000 bytes in length, approximately.

SQWEBMAIL_MAXMSGSIZE
Approximate maximum size, of a message, including the text portion and all attachments (overrides the --with-maxmsgsize parameter to the configure script). There can be any number of attachments, each one up to SQWEBMAIL_MAXATTSIZE bytes long, but the sum total of the entire message cannot exceed SQWEBMAIL_MAXMSGSIZE.

These variables must be set in the environment that runs the webmail CGI program. With Apache, these variables can be set in the httpd.conf file by the SetEnv command. httpd.conf example:

SetEnv SQWEBMAIL_MAXATTSIZE 1000000
SetEnv SQWEBMAIL_MAXMSGSIZE 4000000

NOTE: These settings are global, and apply to all mailboxes. However, advanced Apache configuration can be used to use different environment variable settings with different virtual hosts.

NOTE: On 32-bit platforms, the maximum limits may not exceed 2 gigabytes. A 64-bit platform is required to have SqWebMail capable of handling attachments and messages larger than 2 gigabytes.

Random seed

A random seed is required for preventing certain kinds of external attacks against the SqWebMail server. The random seed must be a constant value, only varying between different instances of SqWebMail. By default the random seed is derived from the inode number of one of the supporting script files. The script file ordinarily remains constant, thus the random seed does not change, but different SqWebMail installs will end up with a different seed.

When a pool of SqWebMail servers is combined for load-balancing, all servers must use the same random seed. This is done by defining the SQWEBMAIL_RANDSEED environment variable. This can be set in the httpd.conf as well:

SetEnv SQWEBMAIL_RANDSEED 82738AZ

SQWEBMAIL_RANDSEED should contain up to ten letters or numbers.

Domain-based templates

The default set of templates for the dynamically generated HTML is installed in /usr/local/share/sqwebmail/html. When the same server is used to provide webmail access for multiple domains it is possible to specify a different set of HTML templates for each domain.

This functionality is not directly implemented in SqWebMail, simply because there is no standard way to specify this. Instead, this is something that will need some minor work set up.

Domain-based templates are implemented by making the web server set the environment variables SQWEBMAIL_TEMPLATEDIR prior to running the sqwebmail binary. The contents of this environment variable override the default location of /usr/local/share/sqwebmail/html. By having the web server initialize this variable based on the domain name it is possible to present different templates, based on the domain name used.

To do this, make copies of the HTML template directory, /usr/local/share/sqwebmail/html. Then, configure the web server to initialize SQWEBMAIL_TEMPLATEDIR appropriately. For example, with Apache:

  <VirtualHost a.b.c.d>
    ServerName webmail.example.com
    [...]
    SetEnv SQWEBMAIL_TEMPLATEDIR /usr/local/share/webmail/webmail.example.com
    [...]
  </VirtualHost>
The possibilities are endless.

Name-based templates

It is now possible to display two or more templates from the same CGI binary WITHOUT setting up multiple domain names.

For example, with Name-based templates an sqwebmail administrator can set up sqwebmail to display a template in the /usr/local/share/sqwebmail/html directory when sqwebmail is called from the URL: http://www.foo.com/cgi-bin/sqwebmail

And display a different template in the /usr/local/share/sqwebmail/alternate-html directory when sqwebmail is called from the URL: http://www.foo.com/cgi-bin/sqwebmail-alt-template

This is made possible by a little web server magic (explained below in the section entitled "Apache Name-based template configuration example") and the setting of TWO sqwebmail environment variables:

SQWEBMAIL_TEMPLATEDIR
SQWEBMAIL_IMAGEURL

You should recognize the SQWEBMAIL_TEMPLATEDIR environment variable from the section above on Domain-based templates. If you haven't read that section yet, please do so now.

The SQWEBMAIL_IMAGEURL environment variable is new in versions of sqwebmail greater than sqwebmail-3.5.3.20030629. It allows us to set, at run time, the image URL, or the root URL, in which to look for our template's images. This image URL is then automatically inserted into the current template anytime a conditional image tag or an IMAGEURL tag is encountered.

This is an example of a conditional image tag:

[#@image.gif, ... @text@#]

The conditional image tag is replaced at template processing time with an HTML <img src="..."> tag if (hence the word "conditional") sqwebmail is set up to display images.

This is an example of an IMAGEURL tag:

[#IMAGEURL#]

The IMAGEURL tag is replaced at template processing time with the contents of the SQWEBMAIL_IMAGEURL environment variable, if set, and otherwise with the value of the --with-imageurl configure option, which defaults to "/webmail".

Apache Name-based template configuration example

Let's take a look at a simple Apache Name-based sqwebmail template configuration example:


  # Sqwebmail Alternate Template URL
  ScriptAlias /cgi-bin/sqwebmail-alt-template "/usr/local/apache/cgi-bin/sqwebmail"

  <Location /cgi-bin/sqwebmail-alt-template>
      Setenv SQWEBMAIL_TEMPLATEDIR "/usr/local/share/sqwebmail/alternate-template"
      Setenv SQWEBMAIL_IMAGEURL "/alternate-webmail"
      [...]
  </Location>

The above should allow your users to run sqwebmail with the template in /usr/local/share/sqwebmail/alternate-template and an image URL of /alternate-webmail, simply by calling sqwebmail from the following URL:

http://www.yourdomain.com/cgi-bin/sqwebmail-alt-template

The original sqwebmail templates would then still be available from this URL:

http://www.yourdomain.com/cgi-bin/sqwebmail

Using Apache's <Location> directive we can utilize a virtually unlimited number of templates without setting up a single virtual domain.

OPTIONAL: Configure webmail calendaring

Optional calendaring services can be enabled in the webmail server. Right now, the current implementation provides basic calendaring services. For more information on calendaring, see the file pcp/README.html.

OPTIONAL: Configure mail filtering for the webmail server

This is an optional feature where the webmail server is used to automatically set up mail filtering rules to forward or deliver incoming mail to folders. This feature requires maildrop to be used as the local mail delivery agent.

Edit the courierd configuration file, and follow the instructions in that file to install maildrop as the local mail delivery agent. Then, follow the instruction below to create the maildirfilter configuration file, which may be installed either in the global configuration file directory (/usr/lib/courier/etc by default), or in each individual Maildir (which overrides the global default).

Implementing mail filtering requires a couple of dominos to fall in the right order. This is not difficult to do, but is a bit tricky. Here's how it works, in general. Specifics follow.

Some people would probably have a difficult time setting it up. That's to be expected. The implementation allows only selected accounts to be set up for mail filtering, so the suggested way is to attempt to set up mail filtering for one account only, test it to make sure it works, then roll it out globally.

The big picture

The maildrop mail filter is used to do the actual mail filtering. maildrop must be installed as your local mail delivery agent. The next thing to do is to actually learn how maildrop works, and learn its filtering language. Although the mail filter will be automaticaly generated here, you still need to become familiar with the filtering language in order to troubleshoot any installation problems. maildrop comes with manual pages documenting the filtering language, as well as some examples. Read them.

The little picture

Here's what's going to happen. The webmail server will automatically generate a maildrop filtering recipe. maildrop reads the recipe, and does its thing. Sounds simple enough, right?

Well, it's not. There are a few little details that need to be resolved.

For starters, the default maildrop filtering recipe is $HOME/.mailfilter. That's how things usually work physical system accounts are used. When virtual mailboxes are installed, things are less murky. There are several ways to set up virtual mailboxes, described elsewhere in this INSTALL file, so the actual implementation varies from system to system. Somehow, the virtual mailboxes share the same physical account, and have the same $HOME. In that case the usual approach is for each virtual mailbox to have the corresponding mail filtering recipe manually specified to maildrop as an extra command line argument. Review the maildrop documentation for more information.

Now, on the other hand, the webmail server doesn't really know anything about physical and virtual accounts. The mapping between a login ID and the maildir is completely encapsulated in the black box-type authentication library. The login ID and password are validated by the authentication library, which obtains the maildir corresponding to the login ID, and the webmail server is started for that maildir. Whether or not a login ID corresponds to an actual system account or to virtual account, that's something the webmail server doesn't really know, or care. All it cares about is the maildir where all the mail is, and that's the end of the story. (The IMAP and POP3 servers work the same way).

So, the issue is that the webmail server needs to find the corresponding maildrop filtering recipe, so it knows where to write the mail delivery instructions. That's the deal

In order for mail filtering to be enabled, it is necessary to initialize the file named maildirfilterconfig in the maildir itself. This is where the webmail server runs, so it simply reads this file. The contents of this file should be as follows:

MAILDIRFILTER=pathtomailfilter
MAILDIR=pathtomaildir

pathtomailfilter specifies the location of the maildrop filtering recipe for this maildir, relative to the maildir itself. Set the current directory to the maildir directory. Now ask yourself, where's my maildrop filtering recipe?

In most cases, where virtual mailboxes are not used, everyone's maildir is $HOME/Maildir, and maildrop uses $HOME/.mailfilter by default. In this case, pathtomailfilter must be set to ../.mailfilter.

When virtual mail accounts are used, this will obviously be something else. The only requirement is that the maildrop filtering recipe and the maildir must be on the same filesystem or partition.

pathtomaildir is the other half of the story. When maildrop gets a message to deliver, maildrop needs to know where the mailboxes and folders are. Maildrop begins running in what it considers to be the recipient's home directory, reading either .mailfilter, by default, or the file specified on the command line.

The webmail server needs to generate filtering instruction that deliver messages to its maildir. By default, the maildir for non-virtual accounts is $HOME/Maildir, so pathtomaildir needs to be set to ./Maildir.

Summary for virtual accounts

Basically, 99% of the time MAILDIRFILTER will be ../.mailfilter and MAILDIR will be ./Maildir. When virtual mail accounts are used, maildrop still must be used as a mail delivery agent. Somehow, the correct maildir that corresponds to the recipient's mail account must be specified as the argument to maildrop. Usually all or most virtual accounts are set up inside a single physical account. In that case it is necessary to set up a different maildrop filtering recipe file for each virtual mail account (since everyone's $HOME/.mailfilter will be the same file), and in each maildir specify the relative path to its corresponding filtering recipe, and the relative path to the maildir from the default home directory. Then, for each virtual mail account, the mail server must run maildrop to do the actual mail delivery, explicitly specifying the filtering recipe to be used.

The global maildirfilterconfig file

In most cases where virtual mail accounts are not used, every maildir's maildirfilterconfig should be the same. As an alternative to installing the same maildirfilterconfig in each maildir, it is possible to install a single maildirfilterconfig systemwide.

Install the global maildirfilterconfig in the Courier mail server's configuration directory (/usr/lib/courier/etc by default).

The global maildirfilterconfig will be used unless maildirfilterconfig exists in the maildir directory. Therefore, the global maildirfilterconfig can be used to provide a default for the majority of the mail accounts, and any exceptions are handled by installing maildirfilterconfig in the maildir directory, whose contents will override the global file.

Happy filtering.

If everything is set up correctly, the webmail menu will present a new link to a screen where mail filtering rules are defined and installed. A mail filter consists of a condition, and an action. A condition is usually based on the contents of some header, or the message body. Regular expressions are allowed. Which means that certain special characters must be quoted. For example, to search for the string "[announce]" verbatim in the subject header, it must be entered as "\[announce\]". Pattern matching, for now, is case-insensitive. The regular expression syntax uses pretty much the same syntax as Perl. See the maildropfilter manual page for more information.

Multiple mail filtering rules can be installed. Their relative order can be rearranged by selecting a filtering rule, then selecting either the "Up" or the "Down" button. It is necessary to select "Save all changes" for any changes to the filtering rules to take effect. Leaving that page in any other way will throw away all changes made.

Webmail runtime configuration

There are some options which can be used to change the webmail server's behavior for individual accounts, or globally, using the "Account Options" feature in the Courier mail server Authentication library. The individual account's setting takes precedence over the DEFAULTOPTIONS settings in the authdaemonrc configuration, so for example if you want to disable webmail access for most accounts but enable it for a select few, you can set DEFAULTOPTIONS="disablewebmail=1" in the authdaemonrc configuration file, and add the option disablewebmail=0 to individual accounts. See the section "Account options" in README_authlib.html in the courier-authlib package for more information on setting the following account options:

disablewebmail - if set to a non-zero value, this account will not be permitted to login to webmail (e.g. because the user is only allowed to use POP3 or IMAP)

wbnochangingfrom - if set to a non-zero value, the webmail server will not allow the From: header to be changed, it will always have its default value.

wbnochangepass - if set to a non-zero value, the webmail server will not allow passwords to be changed. See "Changing mail account passwords using the webmail server", below, for more information.

wbusexsender - if set to a non-zero value, the webmail server will attach an X-Sender: header to all outgoing messages. This can be used in the event you would like to be able to modify the From: header, yet also be able to track sent mail to the original account.

wbnoimages - if set to a non-zero value then no images or icons will be used. The generated interface will be a text-only interface.

wbnodsn - set to a non-zero value then the option to request delivery confirmation receipts will not be shown.

OPTIONAL: Changing mail account passwords using the webmail server

After installing the webmail server be sure to test that the login password can be changed through the webmail server.

If you do not want to use the password change function you can also remove the sqwebpasswd program. This is a helper program, installed with the set-groupid bit set, that relays the password change request to the authentication daemon, through the filesystem socket that is not globally accessible. The password change request consists of the account name, the old password, and the new password. The password change request is validated by the authentication daemon, and the old password must match the existing password on the account, before the password change goes through. This set-groupid helper program is safe to use.

OPTIONAL: Configure autoreplies for the webmail server

Enabling mail filtering, according to the instructions in the previous section, automatically enables MIME autoreply capability. The webmail interface can be used to configure simple autoresponders. By default there is no limit on the number of the size of created autoreplies, therefore it is recommended that a quota be set up on the autoreplies.

An global autoreply quota is set up by initializing the /usr/lib/courier/etc/autoresponsesquota configuration file. This file sets the autoreply quota globally. An autoresponsesquota file in the Maildir will override the global quota setting for that maildir only. See the courier(8) manual page for the description of the autoresponsesquota file.

Autoreplies can include any valid MIME content (MIME content other than plain text can be uploaded). The following special procedure needs to be used to prepare multipart autoreply content, such as text and html alternatives of the same message:

Assign a filename extension to the message/rfc822 MIME content. For example, edit your mime.types file, find the message/rfc822 MIME type (append one if it's not in mime.types), and make sure that it has at least one filename extension, such as "msg".

Prepare the multipart MIME autoreply. The most convenient way is to prepare a normal E-mail message using a conventional E-mail client. Save the RFC822-formatted message in a file with a ".msg" extension, and upload it on the autoreply screen.

Webmail handles uploaded message/rfc822 content by removing all headers except the MIME headers, leaving the MIME content type header, and the actual MIME content.

Normally there is no limit on the number or the total size of autoreplies configured via the webmail server. A quota can be installed by initializing the autoresponsesquota configuration file. See courier(8) for more information.

OPTIONAL: Configure encryption for the webmail server

This is an optional feature in the webmail server that uses GnuPG to send and receive encrypted/signed E-mail. There is no encryption code in the webmail server, it uses GnuPG to do encryption and decryption. For more information on setting up and using encryption, read the file gpglib/README.html in the source distribution.

OPTIONAL: Install automatically-appended footer text for webmail messages

/usr/lib/courier/share/sqwebmail/html/LANG/footer - if this file exists, its contents will be appended to the end of every sent message from the webmail server. The actual directory where sqwebmail's html language files are installed may be different with prebuilt Courier packages. LANG is the language code here, there can be a separate footer per installed language. The footer file carries the following requirements:

OPTIONAL: Quota support

There are two ways to implement a quota on the size of a mail account: filesystem quotas and maildir quotas:

Filesystem quotas

The maximum disk space quota is implemented within the operating system's filesystem support code. Here, the operating system enforces the maximum disk space that can be used by each account. This is the only reliable quota implementation if individual accounts have login access to the mail account. Maildir quotas (see below) are implemented entirely within the maildir support code, and can easily be superceeded by anyone with login access to the mail account. Additionally, mail accounts must all be system accounts. Virtual accounts -- that share the same physical system userid -- cannot usually be support by filesystem-based quotas, because all mail accounts have the same userid and groupid.

The webmail server cannot be used with filesystem quotas. The webmail server creates and maintains, all by itself, a number of database files that are used to quickly index and access messages. If an account exceeds its disk quota, the webmail server will not be able to create and update those database file, which results in a rather spectacular crash. If login access is available, it is possible to log in and manually delete some files to reclaim some disk space. If login access is not available, the administrator will have to manually fix the account -- the webmail server will not even be able to open an existing folder and delete messages in order to free up disk space. There is some good news, though: the IMAP and the POP3 server can still be used to access and delete messages from the mail account. Due to the way that out-of-quota condition is handled by the IMAP server, some IMAP clients may mark any existing messages in the account as unread, but that is a minor glitch that does no harm.

Maildir quotas

The Courier mail server can manually enforce a quota for mail accounts that use maildirs. This quota enforcement is implemented entirely in software, and is available only when maildirs are used. This quota implementation will also work with virtual accounts. Maildir quota support is available only with userdb, LDAP, MySQL and PostgreSQL authentication back-ends. Maildir quotas are supported by IMAP, POP3, and the webmail server. To add a maildir quota with userdb, run the following commands, for example:

userdb account set quota=quota
makeuserdb

Here, account identifies the account to which the quota applies, and quota is the quota specification, as described in the maildirquota(7) manual page.

To implement a quota with an LDAP, MySQL, or a PostgreSQL back end, simply follow the instructions given in the corresponding configuration file.

Account OPTIONS

It is possible to adjust certain parameters on an account-by-account basis. This feature is actually implemented in the Courier mail server Authentication Library. See ACCOUNT OPTIONSin the auth_generic manual page.

OPTIONAL: Configure outbound faxing

Fax sending is disabled by default and must be explicitly enabled, according to the following instructions. After fax sending is enabled, addressing an E-mail message to <5552000@fax> will have this message faxed.

Of course, the necessary hardware and software must be available. The requisite hardware is a class 2 faxmodem attached to a serial port. Additional software, separate from the Courier mail server, must also be installed. The Courier mail server does not handle the actual job of faxing. The Courier mail server only reformats E-mail messages as fax images, and runs mgetty+sendfax to send the fax. The Courier mail server also needs additional software to convert E-mail messages to faxes. All additional software must be separately installed, configured, and tested before enabling faxing in the Courier mail server. Most systems already include the following software as part of the base operating system, so in most cases adding fax support will not actually require any additional software to be installed, only minor reconfiguration of existing software:

mgetty+sendfax

mgetty+sendfax works with most Class 2 faxmodems. The Courier mail server does not use the spooling scripts found in the mgetty+sendfax package. The Courier mail server uses its own mail spool. A fax message is handled no differently than any other E-mail message. The only difference is that the E-mail message is addressed to <phonenumber@fax>.

mgetty+sendfax should be configured with its default settings, EXCEPT as follows:

groff or troff, ghostscript, NetPBM

Conversion of E-mail messages to faxes uses ghostscript, and groff. It should be possible to use the original UNIX troff instead of groff, but this has not been tested. The Courier mail server generates the fax cover page from the contents of the E-mail message's headers. The initial text portion of the E-mail message will appear as fax cover page comments. Note that the initial text portion of the E-mail message must be in plain text, not HTML. E-mail attachments will be converted and attached as additional fax pages. E-mail attachments may contain plain text, Postscript or PDF documents. Other attachments will result in the E-mail message being returned as undeliverable.

On the cover page, the sender's name, the recipient's name, and the fax subject gets taken from the E-mail message's headers. The ability to use non-Latin characters depends on the support from the underlying tools, ghostscript and groff, for the default system locale.

Install the NetPBM library to add the ability to fax GIF, JPEG, and PNG images. Each image will be converted to a single fax page. Images in excess of 1500x1500 pixels (approximately) will be truncated, and color images will be dithered to black-and-white.

Enabling faxing

The configuration file /usr/lib/courier/etc/faxrc must be edited in order to enable faxing. This file sets up the dialing parameters, and the default file disables faxing by rejecting all phone numbers. The configuration file has extensive comments that explain how dialing parameters are set.

Using webadmin to set up fax sending is highly recommended. A proper faxrc will automatically hide all the local daling conventions. Webadmin knows how to generate the dialing configuration for the North American dialing plan, with a configurable area code. Faxes should be addressed to a fixed ten digit area code+phone number address, <nnnxxxxxxx@fax>, which will be converted for dialing from the local area code appropriately. Webadmin can also optionally enable faxing to international 011 phone numbers. Webadmin can also fall back to a bare configuration where all phone numbers are dialed as-is, for locations outside of North America.

Sending faxes

E-mail messages may contain attachments. The Courier mail server combines all attachments in the message into a single fax transmission. Attachment types may be freely mixed. A single message may contain one plain text, and one PDF attachment, for example. It is possible to select certain options, as follows:

These options can be combined: <phonenumber>@fax-lowres-ignore>.

Cover pages

/usr/lib/courier/etc/faxcoverpage.tr is the troff source for the FAX cover page, which includes the first plain text section of the E-mail message. Do not attempt to play with faxcoverpage.tr without a clear understanding of troff. It is safe to make trivial changes (such as replacing the "FACSIMILE COVER PAGE" text).

Dialing

The /usr/lib/courier/etc/faxrc configuration file provides rudimentary phone number rewriting logic (stuff like dialing "9," to get outside line from a PBX). The default faxrc configuration file specifies a typical dialing configuration for the North American numbering plan, with seven digit local phone numbers, and 1+ten digit long distance phone numbers. The area code in the default faxrc configuration file is set to "999", you will need to change it to your area code (there are two places in faxrc where the area code needs to be set).

In general, messages should be addressed to the full ten-digit phone numbers. The local area code will be stripped automatically, and "1" will be dialed before all other area codes. If this is done in practice, local area code changes will only require an update to faxrc, without any need to update the address book.

Comments in the faxrc configuration file explain the format of the phone number rewriting rules, in the event that local phone system customization is required (for example, dialing 9 to get an outside line). Several places in North America now use ten digit local phone number overlays, with 1+ten digit long distance dialing. TODO: Use webadmin if you are not sure how to set this up.

Security

The default faxrc configuration file allows only locally-generated faxes. faxrc must be modified in order to accept faxes via ESMTP.

Additionally, faxes are accepted via ESMTP only if the FAXRELAYCLIENT variable is set. See the makesmtpaccess(8) man page for additional information.

OPTIONAL: Configure inbound faxing

mgetty has an option that runs a script called "new_fax" after it receives a fax. The default location for this script is either /usr/local/lib/etc/mgetty+sendfax/new_fax or /etc/mgetty+sendfax/new_fax. Consult your mgetty documentation to determine if the new_fax option is enabled, and the exact script location.

The Courier mail server provides a script - /usr/lib/courier/share/faxmail/new_fax - that can be used as mgetty's new_fax script. This script converts incoming faxes to PNG images, and delivers it to a local mailbox. Simply copy this script to mgetty's etc directory (or install a soft link there), to automatically drop incoming faxes to a local mailboxes.

The /usr/lib/courier/etc/faxnotifyrc configuration file specifies the mailbox that receives incoming faxes, and several other related options.

OPTIONAL: Install the Courier mail server log analyzer

The Courier mail server log analyzer (the courier-analog package) is a Perl script that generates log summaries for the Courier mail server. The Courier mail server log analyzer generates log summaries for incoming and outgoing SMTP connections, and IMAP and POP3 activity. courier-analog can generate output in text or HTML format.

The Courier log analyzer is not included in the main the Courier mail server tarball, it must be downloaded separately from https://www.courier-mta.org/download.html#analog. After downloading and installing this package, see the courier-analog manual page for more information.

OPTIONAL: Configure Courier IP address-specific settings for servers with multiple IP addresses

When running Courier on a server that has more than one IP address, it's possible to configure Courier to have a "vanity" configuration for each IP address, such as the IP address for outgoing connections for relaying messages received by a client that connects to each address, or its server name that it uses in the "Received:" headers that Courier adds to each message.

See the "Servers with multiple IP addresses" section in the courier(8) manual page for more information.

OPTIONAL: configure hostname-dependent configuration

Several Courier configuration files specify settings that reference the server's fully-qualified domain name. It is possible to have a fixed set of configuration files with the key configuration files using a wildcard placeholder for the system hostname, and replicate these configuration files to multiple servers with externally- assigned hostname (and likely IP addresses), such as DHCP-provided ones; with the server's hostname referenced by the relevant placeholders.

Example: replicate the same set of configuration files to servers assigned hostnames of "mx1" and "mx2", via DHCP, with Courier recognizing its fully-qualified domain name as "mx1.example.com" and "mx2.example.com", respectively.

See the "Hostname-dependent configuration" section of the courier(8) manual page for more information.

Decommission your existing mail server

This step consists of flushing the mail queue of your existing mail server and removing it from the system.

If you're using sendmail, edit your startup script, and start sendmail with the option '-q30m' only. Remove the -bd option. This causes sendmail to stop listening on port 25, and stay as a daemon process only for the purpose of running the queue every 30 minutes.

If you're using Qmail, remove tcpserver from your system startup script.

Wait for all existing mail to flush itself out, then permanently remove your existing server.

Depending on your system, you may need to create a bunch of soft links, such as /usr/bin/sendmail, /usr/sbin/sendmail, /lib/sendmail, or /etc/sendmail that point to /usr/lib/courier/bin/sendmail. If you want to receive mail via UUCP you will also need to make sure that UUCP knows to find rmail in /usr/lib/courier/bin as well.

Sample init script

You're now ready to configure your system to start the Courier mail server at system boot time (and shut it down at system shutdown). If your system uses system-V init scripts, here's a sample script that you can install in your /etc/rc?.ddirectories. This is a slightly modified version of the init script that's used in the Courier RPM or DEB package (courier.sysvinit file in the source code tarball).

NOTE: the following script may take a long time to finish, the very first time it runs. That's because the script automatically creates test SSL certificates the first time the script runs (provided that SSL support is available). This can take as much as 5-6 minutes on a slow machine. Subsequent starts should take only a few seconds.

#! /bin/sh
#
# chkconfig: 2345 35 65
# description: Courier - SMTP server
#
# NOTE: The 'restart' here does a "hard" stop, and a start.  Be gentle, use
# "courierd restart" for a kindler, gentler, restart.
#
#

prefix="/usr/lib/courier"
exec_prefix="/usr/lib/courier"
sysconfdir="/usr/lib/courier/etc"
sbindir="${exec_prefix}/sbin"
libexecdir="/usr/lib/courier/libexec"
datadir="/usr/lib/courier/share"

case "$1" in
start)
        cd /
        # Start daemons.
        touch /var/lock/subsys/courier

        echo -n "Starting the Courier mail server:"

        # Use default DH parameter file, if it does not exist.

        if test ! -f ${datadir}/dhparams.pem
        then
            ln ${datadir}/dhparams.pem.dist ${datadir}/dhparams.pem
        fi

        # First time after install create aliases.dat and makesmtpaccess.dat

        test -f ${sysconfdir}/aliases.dat || ${sbindir}/makealiases

        esmtpdcert=0

        . ${sysconfdir}/esmtpd
        case x$ESMTPDSTART in
        x[yY]*)
                esmtpdcert=1
                ;;
        esac

        test -f ${ACCESSFILE}.dat || ${sbindir}/makesmtpaccess

        . ${sysconfdir}/esmtpd-msa
        case x$ESMTPDSTART in
        x[yY]*)
                esmtpdcert=1
                ;;
        esac

        test -f ${ACCESSFILE}.dat || ${sbindir}/makesmtpaccess-msa

        ${sbindir}/courierfilter start
        echo -n " courierfilter"

        if test -x ${sbindir}/courierldapaliasd
        then
                ${sbindir}/courierldapaliasd start
                echo -n " courierldapaliasd"
        fi

        if test -f ${libexecdir}/courier/sqwebmaild
        then
                ${sbindir}/webmaild start
                echo -n " webmail"
        fi

        ${sbindir}/courier start
        echo -n " courierd"

        if test "$esmtpdcert" = 1
        then
# If we do not have a certificate, make one up.

                if test ! -f ${datadir}/esmtpd.pem
                then
                        if test -x $COURIERTLS
                        then
                                echo -n " generating-ESMTP-SSL-certificate..."
                                ${sbindir}/mkesmtpdcert >/dev/null 2>&1
                        fi
                fi
        fi

        . ${sysconfdir}/esmtpd
        case x$ESMTPDSTART in
        x[yY]*)

                ${sbindir}/esmtpd start
                echo -n " esmtpd"
                ;;
        esac

        . ${sysconfdir}/esmtpd-msa
        case x$ESMTPDSTART in
        x[yY]*)

                ${sbindir}/esmtpd-msa start
                echo -n " esmtpd-msa"
                ;;
        esac

        if test -x ${sbindir}/pop3d
        then
                POP3DSTART=""
                POP3DSSLSTART=""

                if test -f ${sysconfdir}/pop3d
                then
                        . ${sysconfdir}/pop3d
                fi
                case x$POP3DSTART in
                x[yY]*)
                        ${sbindir}/pop3d start
                        echo -n " pop3d"
                        ;;
                esac
                if test -f ${sysconfdir}/pop3d-ssl
                then
                        . ${sysconfdir}/pop3d-ssl
                fi
                case x$POP3DSSLSTART in
                x[yY]*)
                        if test -x $COURIERTLS
                        then
# If we do not have a certificate, make one up.

                                if test ! -f ${datadir}/pop3d.pem
                                then
                                        echo -n " generating-POP3-SSL-certificate..."

                                        ${sbindir}/mkpop3dcert >/dev/null 2>&1
                                fi

                                ${sbindir}/pop3d-ssl start && \
                                        echo -n " pop3d-ssl"
                        fi
                        ;;
                esac
        fi

        if test -x ${sbindir}/imapd
        then
                . ${sysconfdir}/imapd
                case x$IMAPDSTART in
                x[yY]*)
                        ${sbindir}/imapd start
                        echo -n " imapd"
                        ;;
                esac
                . ${sysconfdir}/imapd-ssl
                case x$IMAPDSSLSTART in
                x[yY]*)
                        if test -x $COURIERTLS
                        then
# If we do not have a certificate, make one up.

                                if test ! -f ${datadir}/imapd.pem
                                then
                                        echo -n " generating-IMAP-SSL-certificate..."

                                        ${sbindir}/mkimapdcert >/dev/null 2>&1
                                fi

                                ${sbindir}/imapd-ssl start && \
                                        echo -n " imapd-ssl"
                        fi
                        ;;
                esac
        fi

        if test -x ${bindir}/webmlmd
        then
                . ${sysconfdir}/webmlmrc
                if test "$LISTS" != ""
                then
                        ${bindir}/webmlmd start ${sysconfdir}/webmlmrc && \
                                echo -n " webmlmd"
                fi
        fi

        echo ""
        ;;
stop)
        echo -n "Stopping the Courier mail server:"

        if test -x ${bindir}/webmlmd
        then
                ${bindir}/webmlmd stop ${sysconfdir}/webmlmrc
                echo -n " webmlmd"
        fi

        if test -x ${sbindir}/imapd
        then
                ${sbindir}/imapd stop
                echo -n " imapd"
        fi

        if test -x ${sbindir}/imapd-ssl
        then
                ${sbindir}/imapd-ssl stop
                echo -n " imapd-ssl"
        fi

        ${sbindir}/esmtpd-msa stop
        echo -n " esmtpd-msa"

        ${sbindir}/esmtpd stop
        echo -n " esmtpd"

        if test -x ${sbindir}/pop3d
        then
                ${sbindir}/pop3d stop
                echo -n " pop3d"
        fi

        if test -x ${sbindir}/pop3d-ssl
        then
                ${sbindir}/pop3d-ssl stop
                echo -n " pop3d-ssl"
        fi

        ${sbindir}/courier stop
        echo -n " courierd"

        if test -f ${libexecdir}/courier/sqwebmaild
        then
                ${sbindir}/webmaild stop
                echo -n " webmail"
        fi

        if test -x ${sbindir}/courierldapaliasd
        then
                ${sbindir}/courierldapaliasd stop
                echo -n " courierldapaliasd"
        fi

        ${sbindir}/courierfilter stop
        echo " courierfilter"
        ;;
restart)
        $0 stop
        $0 start
        ;;
esac
exit 0

The reason I test for the existence of the POP3 and IMAP server binaries is because I build the POP3 and IMAP servers as separate sub-packages, that do not have to be installed. These tests avoid the need for each sub-package to install its own startup script.