Courier Mail Server

This file contains one line, containing the home directory of the account that's used for filtering mail addressed to local alias lists.

When mail filtering is enabled, local recipients have the ability to define mail filters which can selectively reject unwanted mail. /etc/courier/aliases may define local mail aliases that contain one or more recipients. If it is desired to use local mail filtering for mail addressed to an alias address, designate a local account that will be used to specify filtering instructions, and put its home directory into this control file. The filtering argument will be "alias-address" where address is the name of the alias. See localmailfilter(7) for more information.

Due to technical limitations, content filtering is not available for multiple-recipient aliases.

Changes to this file take effect immediately.

This file sets the systemwide quota on autoreplies, if autoreplies and mail filtering are enabled. Note that this can only really be effective if there is no login access to the mail account, since this autoreply quota can be trivially overriden.

The autoresponsesquota file contains one line: "Cnnn" or "Snnn" (or both strings, on the same line). Cnnn: allow up to #nnn autoreplies to be created. Snnn: allow up to #nnn bytes as the total size of all autoreplies, combined. If both Cnnn and Snnn are specified, both quotas apply. If this file does not exist, there is no limit on autoreplies. This quota setting applies systemwide. To override the quota setting for a particular Maildir, create the autoresponsesquota file in that Maildir (which takes precedence).

This file contains one line, containing a name of a machine where mail will be rerouted if it cannot be immediately delivered. Spaces are not allowed in this file.

Mail gets rerouted if it cannot be delivered after the time interval specified by the warntime configuration file. When backuprelay is provided a delayed delivery status notification will NOT be generated. The message will be rerouted even if the recipient's delivery status notification setting does not include a delayed notification request.

This feature is intended for use by relays that handle large quantities of mail, where you don't want to accumulate a large mail queue for unreachable mail servers. Please note that ALL undeliverable mail will be rerouted in this fashion. Even if the recipient of a message is a local recipient - and the recipient's mail filter is rejecting the message with a temporary error code - the message will still be rerouted if it's undeliverable after the specified amount of time.

Although currently SMTP is the only meaningful application for this feature, the Courier mail server is a protocol-independent mail server, and the backup relay function can be extended to other protocols, as they become available.

Multiple backup relays can be used by simply assigning multiple IP addresses to the same machine name. Note that the Courier mail server checks for both MX and A records for the machine specified in this configuration file.

It's important to note that when this setting is specified, warning messages get turned off for all messages, including messages addressed to local recipients. If a temporary delivery error prevents a message from being delivered to a local mailbox, it remains in the queue until the temporary error condition gets cleared. Normally, if the message remains in the queue beyond the warning interval, the warning message gets generated. When this setting is specified, the warning message gets replaced with a forward to the backup relay, but this occurs only for messages that are delivered via SMTP.

This file contains one line, containing a single number. This number specifies the absolute maximum number of recipients for a single message. If the Courier mail server receives a message with more recipients, the message is duplicated as often as necessary until each copy of the message has no more than batchsize recipients. If batchsize is missing, it defaults to 100 recipients per message.

This configuration file configures domain-based junk mail filters. Lines in this configuration files that begin with the # character are considered comments, and are ignored. The remaining lines contain the following directives, in any order:

This configuration file enables basic calendaring features in the webmail server. Calendaring is currently considered experimental in nature, and the current implementation provides basic calendaring services. If this file does not exist, calendaring options are disabled. If this file exists it should contain a single word: "local". For example:

echo "local" >/etc/courier/calendarmode

This configuration file must be globally readable, so make sure that your umask is not set too tight.

This configuration file specifies several parameters relating to general the Courier mail server configuration. A default configuration file will be installed, and you should consult its contents for additional information.

This file contains one line whose contents is a valid mail domain. Most header rewriting functions will append @defaultdomain to all E-mail addresses that do not specify a domain. If defaultdomain is missing, the Courier mail server uses the contents of the me control file.

When the ESMTP server receives a “RCPT TO” command containing the address <user@[ip.address]>, and the IP address is the same as the IP address of the socket it's listening on, the ESMTP server replaces the IP address with the contents of the defaultdomain control file. If defaultdomain is missing, the Courier mail server uses the contents of the me control file.

The contents of defaultdomain are also appended to return addresses to mail sent from the Courier mail server's webmail server, if they don't already have a domain. If defaultdomain does not exist, the Courier mail server's webmail server obtain the machine hostname, and uses that.

This file contains one line whose contents specify the name of dot-files in users' home directories which contain delivery instructions. If this file does not exist, the Courier mail server reads $HOME/.courier, $HOME/.courier-foo, $HOME/.courier-default, and so on. If this file contains the text "qmail", the Courier mail server will instead read $HOME/.qmail, $HOME/.qmail-foo, $HOME/.qmail-default, and so on.

This file contains one line specifying the contents of the From: header that the Courier mail server puts in all delivery status notifications. This file specifies a complete header, except for the "From: " part. If dsnfrom is missing, then the Courier mail server uses the following header: "Courier mail server mail server at me" <@>

Maximum size, in bytes, of a message whose contents are included in delivery status notifications. By default, the entire message is only included in non-delivery notices (failures). Only the headers will be returned for delay notifications (warnings) and return receipts; or for failures if the original message is larger than dsnlimit. If missing, dsnlimit is set to 32K.

The sender can request that the entire message be returned even on delayed notices or return receipts, however the Courier mail server will ignore this request if the message size exceeds this limit.

This configuration file enables the global mail filtering API for selected mail sources. This file, if it exists, contains a single line of text that specifies which kind of mail will be filtered. The possible values are:

If you want to specify more than one source of mail, such as ESMTP and local mail, specify both esmtp and local, separated by a space character.

This file lists all domains that the Courier mail server accepts mail for via ESMTP. This file is in the same format as the locals file. If this file is missing, the Courier mail server uses the single domain specified in me (or the system machine name).

See the section called “Hostname-dependent configuration” for more information on hostname-dependent configuration in the esmtpacceptmailfor configuration file.

esmtpacceptmailfor.dat is a binary database file that lists additional domains that the Courier mail server accepts mail for, just like esmtpacceptmailfor. The binary database file will be faster than a flat text file with a large number of domains. The Courier mail server accepts mail for domains listed in either esmtpacceptmailfor or esmtpacceptmailfor.dat. esmtpacceptmailfor.dat is created by the makeacceptmailfor command from the contents of the esmtpacceptmailfor.dir directory. You can use both esmtpacceptmailfor.dat and esmtpacceptmailfor at the same time. Put your most popular domains in esmtpacceptmailfor, and put the rest of them into esmtpacceptmailfor.dat.

See the section called “Hostname-dependent configuration” for more information on hostname-dependent configuration in the esmtpacceptmailfor.dir configuration files.

This configuration file configures ESMTP authentication for the ESMTP client. This is a text file of zero or more lines that contain the following fields:

relay userid password

When the Courier mail server connects to a remote ESMTP relay, the Courier mail server will authenticate itself using userid and password. These fields are separated by one or more whitespace characters. Because this file contains passwords, it must not be world or group readable, and owned by the user "daemon".

ESMTP negotiation will take place, and the Courier mail server will use a SASL authentication method supported by both the Courier mail server and the remote ESMTP server. Currently the Courier mail server supports PLAIN, LOGIN and CRAM-MD5 authentication. CRAM-MD5 is preferred over the other two, and PLAIN is preferred over LOGIN.

The Courier mail server also supports ESMTP over SSL (the ESMTP STARTTLS extension). If ESMTP STARTTLS is enabled, STARTTLS will be used to establish a secure link first. The authentication will take place afterwards, over a secure channel.

Changes to this file take effect, more or less, immediately (existing connections are not affected, but new connections will read the updated data).

This file is used to initialize the environment and parameters for courieresmtpd. A default file will be provided during installation. See the comments in the file for more information. For changes to this file to take effect you run the esmtpd stop command followed by esmtpd start.

This file contains one line of text that specifies how long courieresmtp waits after a failure to contact the remote mail server before another attempt is made. courieresmtp (not to be confused with courieresmtpd) delivers outgoing mail to remote mail servers. The timeout is specified as an integral number, optionally followed by m - minutes, or h - hours. Otherwise it is specified in seconds.

The courieresmtp process delivers mail that's routed to external mail relays, via ESMTP. When attempting to initally contact a mail server courieresmtp waits for the amount of time specified by esmtptimeoutconnect (see below). esmtptimeoutconnect is usually set to a relatively long period of time, in order to accomodate slow mail servers. A large number of messages queued up for an unreachable mail server can tie up delivery slots that can be put to a better use by reassigning them for mail to another domain. Although the Courier mail server does not usually assign all delivery slots for messages to the same domain (this is a tuneable parameter), it is still not very healthy to have a bunch of courieresmtp daemons spinning their wheels, doing nothing.

The situation worsens when there is a large number of mail relays that accept mail for the same domain, and all of them are unreachable due to a network failure. That's because the esmtptimeout waiting period is used for each individual mail relay. Multiply esmtptimeout by the number of servers to see how large the delay really will be.

esmtpdelay is implemented internally in the courieresmtp module. The main the Courier mail server scheduling daemon is not aware of what's happening internally in courieresmtp. When courieresmtp fails to contact any mail relay for the domain, the message is postponed, and the esmtpdelay timer is set. Any additional messages received by the same courieresmtp daemon (for the same domain), are immediately postponed without any attempt to contact a remote mail relay. When the amount of time set by esmtpdelay expires, courieresmtp will attempt to make another delivery attempt as usual.

If esmtpdelay does not exist, the default delay is five minutes. Any messages that are postponed look like any other temporary failure to courierd. Delivery attempts are rescheduled as if a real temporary failure took place. Therefore it does not make sense to set esmtpdelay to be greater than retryalpha (see below). When retryalpha is smaller is esmtpdelay, you'll just messages spinning through the mail queue, with useless delivery attempts being attempted because esmtpdelay still hasn't expired.

Occasionally you might observe somewhat strange behavior on systems with heavy mail traffic. esmtpdelay applies separately to each individual instance of courieresmtp. When a remote mail server keeps going up and down, it is possible to end up with multiple courieresmtp daemons handling mail for the same domain, but only some of them will encounter a network failure, purely by the luck of the draw. The remaining daemons will be able to establish a connection. So you'll end up with some courieresmtp daemons being able to deliver mail immediately, while the rest are still waiting patiently for esmtpdelay to expire, postponing all messages in the meantime. Some messages - but not all - will be immediately postponed without a delivery attempt, becauses they ended up getting to a daemon which is waiting for esmtpdelay to expire.

Another anomalous situation may happen when a courieresmtp daemon gets reassigned to another domain, and then receives more mail for the previous domain. This can happen when you have a lot of mail going through. Although the Courier mail server tries to shuffle all mail for same domain into one pile, the scheduler still tries to dispatch mail on "first-come, first-serve" basis, as much as possible. When that happens another delivery attempt will be made immediately, because the previous esmtpdelay was cancelled when the daemon got reassigned to another domain.

There can also be occasional abnormalities that affect systems with light traffic. When there is a domain with several mail relays of equal priority, one mail relay is chosen at random for the connection attempt. If some of the equal-priority mail relays are unreachable and a courieresmtp daemon picks it, it will start the esmtpdelay timer and refuse to deliver any more mail until it expires, even if most of the mail servers are functional. This will happen only with mail relays of the lowest priority. Otherwise, courieresmtp will always try to contact another mail relay of a still lower priority, before giving up and setting the esmtpdelay timer. Another courieresmtp daemon will not be started for the same domain if there's already an existing one, so all delivery attempts will be turned away until esmtpdelay expires. Another courieresmtp daemon will be started only in the event of multiple simultaneous delivery attempts that happen to coincide at the same time.

This is somewhat mitigated by the fact that all courieresmtp daemons are killed after a short period of total inactivity (currently one minute), so that longer intervals specified by esmtpdelay are ignored. Note, however, that receiving a message to deliver, and then postponing it immediately, does count as some activity.

esmtpdelay can be turned off by setting it to 0 seconds. esmtpdelay is designed for servers that handle heavy amount of mail that wish to avoid having outbound delivery slots tied up due to network failures, at an expense of an occasional anomalous behavior due to harmless paranoia. esmtpdelay may prove to actually make things worse for systems that carry only light mail traffic, if they are burdened with a task of exchanging mail primarily with external systems that are not properly maintained.

The complete greeting banner displayed by courieresmtpd. Changes to this file take effect immediately.

This file contains one line of text, what the Courier mail server calls itself in the EHLO or HELO command sent to a remote SMTP server. me is used if this file does not exist.

esmtphelo may also be set to a special value of “*”:

echo '*' >esmtphelo

(Note the single quotes, to prevent “*” from being expanded by the shell). The Courier mail server will take the IP address of the local side of the connection to the remote SMTP server, look up the IP address in DNS, and use the hostname from the reverse DNS lookup. This might be useful when the Courier mail server server is multihomed. The Courier mail server will look up the local IP address of each individual connection, and use that in its EHLO or HELO command.

This file is used by the ESMTP module, and it contains one or more lines in the following form:

domain:relay[,port][/SECURITY=STARTTLS][/SECURITY=REQUIRED][/SECURITY=SMTPS]

domain is any SMTP domain. relay specifies a fixed mail relay for this domain. relay is optionally followed by a comma and a port number, to specify a port other than the default port 25. If an address's domain is not found in esmtproutes, the Courier mail server looks for MX and A records as usual (and always delivers to port 25). If the domain is found in esmtproutes, however, any MX or A records for the domain are ignored; instead the Courier mail server delivers the message to the specified relay.

relay can be another domain, or an explicit IP address inside brackets. For example, if esmtproutes contains the following:

example.com: relay.domain.com
domain.com: [192.168.0.2]

Mail for example.com is delivered to relay.domain.com, ignoring any MX records for example.com. Mail for domain.com will be delivered to the machine at IP address 192.168.0.2. All other domains will have their MX and A records looked up.

esmtproutes may contain comments, any line that starts with the # character is ignored. Also, wildcards are allowed:

 .example.com: [192.168.0.3],26

This specifies that any address of the form <anything@anything.example.com> will be delivered to the mail server at this IP address, but on port 26.

esmtproutes is read from top to bottom, stopping as soon as a first match is found.

domain may be empty, this specifies a smarthost for all domains. For example, if esmtproutes contains the following text:

example.com: relay.example.com
        :[192.168.0.4]

This specifies that all mail to example.com is rerouted to relay.example.com. All other mail is routed to the IP address 192.168.0.4.

If relay is empty, the Courier mail server interprets it as an explicit directive to use MX and A records from DNS. For example:

example.com:
:[192.168.0.4]

This uses MX and A records for all messages to example.com. All other mail is rerouted to the IP address 192.168.0.4.

The /SECURITY=STARTTLS flag indicates that mail to this domain will use the SECURITY ESMTP extension. See the Courier mail server installation notes for a description of SECURITY, what it does, and how to configure it.

/SECURITY=SMTPS uses an encrypted SMTP connection. This is an alternative to STARTTLS. Encrypted SMTP uses a different port, port 465, which must be specified explicitly:

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

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

A combination of broken mail servers written by incompetent programmers, and poorly-managed Internet providers will result in a mail server that advertises the ability to use an encrypted connection to receive mail, but either disconnect immediately, or return an error message when the sender takes up the receiver's offer to do so.

When the Courier mail server connects to another server that claims to support an encrypted connection, tries to enable it, then fails because the other mail server drops the connection or returns an error message, all subsequent connection attempts to the same mail server will ignore the server's false advertising, and proceed to send mail without attempting to enable encryption. The Courier mail server remembers not to use the encryption with this server for the next 2-4 hours (depending on an internal log file's rotation schedule). Once the remote mail server emerges from the penalty box, the next connection attempt will try again, and see if it's still doesn't work.

The /SECURITY=REQUIRED flag blocks the Courier mail server from sending mail to the remote server unless a standard encryped connection can get established. If it's known that the given mail server should only receive encrypted mail, /SECURITY=REQUIRED prevents a man-in-the-middle attack where the remote mail server's advertisement of is STARTTLS capability gets suppressed, and the mail gets sent in the clear.

To summarize:

Changes to esmtproutes take effect immediately, more or less. Existing courieresmtp processes that already have an established connection will ignore any changes.

This file contains one line of text that specifies the timeout for an SMTP command. The timeout is specified as an integral number, optionally followed by m - minutes, or h - hours. Otherwise it is specified in seconds. This timeout is used for all SMTP commands, unless the SMTP command has a dedicated timeout defined by a different configuration file. The default timeout is ten minutes.

This file contains one line of text that specifies the timeout for an SMTP connection attempt. Most TCP/IP stacks wait an extraordinary long period of time for SMTP connections to go through. This configuration setting limits the amount of time the Courier mail server waits for the SMTP connection to complete. The default timeout is one minute. Set esmtptimeoutconnect to 0 in order to use whatever default timeout your TCP/IP stack uses.

This file contains one line of text that specifies the timeout for transferring the message contents or individual replies. The default timeout is five minutes. You WILL HAVE TO bump this up if you're on a slow link, and you want to send large messages. A 28.8Kbps link can be optimistically expected to push 3,000 bytes per second. With a five minute cutoff, you will not be able to send or receive anything larger than about 870 Kb. You have no business sending or receiving 870 Kb messagesl, if all you have is an analog 28.8Kbps connection.

This file contains one line of text that specifies the timeout for the initial EHLO or HELO command. The Courier mail server will wait this amount of time to receive the initial greeting banner from the remote SMTP server, and a response to the subsequent EHLO/HELO command. The default value is 5 minutes.

This file contains one line of text that specifies how often outbound SMTP sessions are kept idle after delivering a message. After the Courier mail server connects to an SMTP server and completes the attempt to deliver the message, the SMTP session is kept idle for this time interval before being shut down. If the Courier mail server receives another message for the same domain, it will be delivered using the existing SMTP session, instead of establishing a new one. Note that some SMTP servers have a very short idle timeout, Qmail's is only two minutes. The default value is 60 seconds.

Note that there's also a separate limit to the maximum number of simultaneous SMTP sessions to the same domain. That limit is currently four, which is adequate for nearly every situation, so for now it will be set by an undocumented configuration file.

This file contains one line of text that specifies how often the Courier mail server will issue a useless RSET command when the connection is idle (see esmtptimeoutkeepalive). While waiting for any more messages to deliver to the same domain, or for the esmtptimeoutkeepalive interval to expire, courieresmtp will transmit RSET commands at regular intervals specified by this configuration file. The default value is 0 seconds, which turns off the keepalive ping altogether. This configuration settings must be for a shorter time interval than esmtptimeoutkeepalive for it to make any sense. Note that other system administrators may consider this to be a very rude thing to do. Also keep in mind that this may generate quite a bit of idle traffic. If you have the Courier mail server configured for a maximum number of 200 outbound SMTP sessions and a 30 second esmtptimeoutkeepaliveping setting, then you can have as much as an average of around seven pings every second!

This file contains one line of text that specifies how long the Courier mail server waits for the external SMTP server to acknowledge the QUIT command, before the Courier mail server unilaterally tears down the connection. The default value is 10 seconds. This must be a small value because the Courier mail server needs to be able to shut down quickly, on very short notice.

This file specifies how long the Courier mail server normally tries to repeatedly resend a fax message (if the courierfax module is enabled). The default E-mail message retry timeout (the queuetime setting) is one week, which is a reasonable timeout value for E-mail messages (taking into account downed circuits, or crashed servers). However, it doesn't make sense to keep trying to redeliver fax messages for a whole week.

faxqueuetime specifies the timeout for fax messages. This time interval is specified in the same way as queuetime (see queuetime for more information).

This file specifies which mailbox the Courier mail server should deliver received faxes (if this option is enabled). See the Courier mail server's installation notes for more information.

This file configures the Courier mail server's outbound faxing and dialing parameters. Consult the comments in the default file for additional information, and the courierfax(8) manual page for more information.

This file lists locally-hosted domains. It is very similar in function to the locals control file. Any address with a domain listed in hosteddomains is considered to be a local address. The difference between hosteddomains and locals is that domains listed in hosteddomains are not removed from individual addresses before looking up the location of their mailboxes. For example, if the domain "example.com" appears in locals, the address user@example.com will have example.com removed, and then the Courier mail server will look for a local mailbox named "user".

If the domain "example.com" appears in hosteddomains instead, the Courier mail server will look for a local mailbox named "user@example.com" instead.

The contents of the hosteddomains configuration file is a list of domains, one per line, in lowercase. You must run the makehosteddomains command, followed by courier restart (this restarts the server) for any changes to take effect.

Additionally, hosteddomains can specify simple domain aliases. See the complete description in the makehosteddomains(8) manual page.

See the section called “Hostname-dependent configuration” for more information on hostname-dependent configuration in the locals configuration file.

Non-default IP addresses to send outgoing ESMTP messages from. See the section called “Servers with multiple IP addresses” and the section called “Simulating a server with multiple IP addresses”, below, for more information.

This file is used by the webmail server. It contain a default systemwide list of accessible LDAP address books. 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 the 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).

This file is used by the courierldapaliasd process. See courierldapaliasd(8) for more information.

If this file exists, the Courier mail server will not distinguish being lowercase and uppercase local accounts, so that john@example.com and John@example.com will refer to the same local mailbox (where example.com is your domain). Postmaster, postmaster, and POSTMASTER always refer to the same account, even if locallowercase does not exist.

This file contains one or more lines of text, where each line contains a valid mail domain. Any E-mail address without @domain, or with a domain that can be found in locals will be considered to be an address of a local mailbox. A domain can be specified with a leading dot:

 .domain.com

This is called a "wildcard". Any domain ending in domain.com, such as a.domain.com, b.domain.com, a.b.c.domain.com - but NOT somedomain.com - will be considered local. Note that domain.com is NOT included in this wildcard. Both "domain.com" and ".domain.com" should be listed.

Specific hosts can be excluded from the wildcard. Example:

 !host.domain.com
 .domain.com

anything.domain.com is considered to be a local domain, except for host.domain.com. Note that "!host.domain.com" must appear in locals before the .domain.com wildcard.

The "!hostname" syntax is also valid in the esmtpacceptmailfor control file.

If locals does not exist, the Courier mail server uses the contents of the me control file (note that me specifies only one domain, second and subsequent lines are ignored). Also, see hosteddomains.

See the section called “Hostname-dependent configuration” for more information on hostname-dependent configuration in the locals configuration file.

This file specifies the watchdog timer for local mail deliveries. If a local mail delivery attempt does not complete in the proscribed time interval, the delivering process ID is killed. The time interval in localtimeout is specified in the same way as queuetime (see queuetime for more information).

If this file exists then the webmail login screen will have a drop-down list whose contents will be read from this file. This file should contain a list of E-mail domains, one per line. It should be created if the Courier mail server's webmail server is used to provide mail access for more than one domain. Instead of typing "user@domain" to log in, it will only be necessary to enter "user", and select the domain from the drop-down list. If this file does not exist it will be necessary to enter the full E-mail address into the webmail login screen.

This file, if exists, sets the global defaults for mail filtering in the webmail server. Mail filtering in the webmail server is a subject worthy of special mention. A full description of how to install and configure webmail-based mail filtering is included in the installation notes for the Courier mail server. Refer to the installlation instructions for additional information.

This file, if exists, specifies the location of shared maildirs for the webmail and IMAP server. Normally, each mailbox must be separately configured to access every shared maildir, by the maildirmake(1) command. This file allows shared maildirs to be set globally for everyone. Everyone's webmail and IMAP server will pick up the shared maildirs specified in this file. See maildirmake(1) for more information.

This file contains one line whose contents is a pathname to the maildrop(1) mail delivery agent. If the Courier mail server knows that the delivery agent used to delivery mail locally is maildrop(1) then certain delivery optimizations are possible. This configuration file does NOT actually specify that maildrop(1) should be used as a local mail delivery agent, it only specifies where maildrop(1) is installed. The default local mail delivery instructions are specified in the courierd configuration file. If the specified delivery instruction specify running an external program whose pathname matches the one specified by this configuration file, the Courier mail server assumes that it's maildrop(1), and will use maildrop-specific options to optimize mail delivery.

This configuration file is initialized, by default, to point to the version of maildrop(1) that's integrated with the Courier mail server. The integrated version of maildrop(1) is configured slightly differently than the standalone version of maildrop(1).

Although you can set the maildrop configuration file to point to some other version of the maildrop mail filter, you MUST set the maildropfilter configuration file (see below), to point to the integrated version of maildrop.

This file contains one line whose contents is a pathname to the maildrop(1) mail delivery filter. In addition to being a delivery agent, maildrop can also be used as a mail filtering engine. If this file exists, the Courier mail server will be capable of invoking recipient-specified mail filters when a message is received. If the mail filtering rules reject the message, the Courier mail server will not accept the message for delivery. This means that when receiving mail via ESMTP, the Courier mail server will reject the ESMTP transaction without even accepting the message from the remote mail server.

This file is not installed by default. To activate mail filtering for local recipients, simply copy the contents of the maildrop configuration file to maildropfilter.

This file contains systemwide mail filtering instructions for maildrop(1) deliveries. This configuration file is optional, and is used by maildrop(1) when it is invoked as a traditional post-delivery mail filter. See maildropfilter(6) for more information.

This file contains one line whose contents is a fully-qualified domain name. When a single installation of the Courier mail server is shared over a network, each machine that's running the Courier mail server must have a unique me file. A missing me defaults to the gethostname() system call (see the section called “Hostname-dependent configuration” for more information on hostname-dependent configuration).

If a message does not have a Message-ID: header, the Courier mail server may decide to create one. The host portion of the new header will be set to the contents of msgidhost, which contains one line of text. If msgidhost does not exist, me will be used in its place. Changes to this file take effect immediately.

The Courier mail server's webmail server lets the contents of the From: header be set for mailed messages. If this configuration file exists, the ability to set the contents of the From: header is disabled.

These configuration settings tune the Courier mail server's mail queue processing. The Courier mail server does not load the entire mail queue metadata in memory. queuelo contains a number that specifies the queue “low watermark” message count. queuehi contains a number that specifies the queue “high watermark” message count. queuefill specifies a time interval, “queue refill” in seconds. The number in queuefill may optionally be followed by "m", indicating that the queue refill is specified in minutes.

queuehi specifies the maximum number of messages that are loaded into memory. The Courier mail server reads the mail queue on disk until either it reads all of it, or it reads the number of messages specified by queuehi. As messages are delivered they are removed from the memory and disk. Messages that are deferred for another delivery attempt are removed from memory, but kept on the disk.

When the number of messages in memory falls below queuelo, The Courier mail server goes back to disk and attempts to fill the memory queue to the top, again.

This is, basically, a capsule summary of the mail queue processing logic. Many small, low level details are omitted; this is just an executive overview. When new messages arrive during a large mail backlog, the new messages are also loaded into the memory queue, if there's room for them. Therefore, during a large mail backlog the Courier mail server simultaneously tries to clear the existing backlog, and process any new mail at the same time. Up to the Courier mail server 0.41, all of this generally translates to the Courier mail server giving priority to newly arrived mail, and processing the backed up mail queue if spare resources are available.

The queuefill setting was added in the Courier mail server 0.42, in an attempt to keep new mail from excessively delaying existing mail during a major queue backup. queuefill specifies a time interval. When the Courier mail server completely fills the memory queue it sets a timer. After the interval given by queuefill The Courier mail server will go back and re-fill the mail queue even if the number of messages did not fall below the low watermark. If the Courier mail server finds older messages in the mail queue they will be pushed to the top of the scheduling queue, and given priority.

Smaller queuefill time intervals means more frequent trips to the disk, and more overhead. But, in exchange for that, during a mail backlog the Courier mail server will spend more time handling a greater number of delayed messages. Larger queuefill time intervals means less frequent trips to the disk, and less overhead, in exchange for less "fairness" during large mail backlogs.

queuefill defaults to five minutes, if not specified. Explicitly setting it to 0 seconds turns off the queue re-filling completely, essentially reverting to pre-0.42 behavior. The default queuelo and queuehi values are computed at run time. queuelo defaults to the larger of 200, and the sum total of configured mail delivery slots, both local and remote. queuehi, if not explicitly set, defaults to the smaller of twice the queuelo, or queuelo plus 1000.

This file specifies how long the Courier mail server normally tries to repeatedly deliver a message, before giving up and returning it as undeliverable. Messages are immediately returned as undeliverable when a permanent failure is encountered (such as the recipient address not being valid). Attempts to deliver the message when there's a temporary, transient, error (such as the network being down) will be repeatedly made for the duration of time specified by this configuration file. This file contains a number followed by the letter 'w' for weeks, or 'd' for days. It is also possible to use 'h' for hours, 'm' for minutes, or 's' for seconds. Only integers are allowed, fractions are prohibited. However, you can use '1w2d' to specify one week and two days. If queuetime is missing, the Courier mail server makes repeated delivery attempts for one week.

These control files specify the schedule with which the Courier mail server tries to deliver each message that has a temporary, transient, delivery failure. retryalpha and retrygamma contain a time interval, specified in the same way as queuetime. retrybeta and retrymaxdelta contain small integral numbers only.

The Courier mail server will first make retrybeta delivery attempts, waiting for the time interval specified by retryalpha between each attempt. Then, the Courier mail server waits for the amount of time specified by retrygamma, then the Courier mail server will make another retrybeta delivery attempts, retryalpha amount of time apart. If still undeliverable, the Courier mail server waits retrygamma*2 amount of time before another retrybeta delivery attempts, with retryalpha amount of time apart. The next delay will be retrygamma*4 amount of time long, the next one retrygamma*8, and so on. retrymaxdelta sets the upper limit on the exponential backoff. Eventually the Courier mail server will keep waiting retrygamma*(2^retrymaxdelta) amount of time before making retrybeta delivery attempts retryalpha amount of time apart, until the queuetime interval expires.

The default values are:

This results in the Courier mail server delivering each message according to the following schedule, in minutes: 5, 5, 5, 15, 5, 5, 30, 5, 5, 60, 5, 5, then repeating 120, 5, 5, until the message expires.

Maximum size of the message, in bytes, that the Courier mail server accepts for delivery. The Courier mail server rejects larger messages. If sizelimit is set to zero, The Courier mail server accepts as large message as available disk space permits. If the environment variable SIZELIMIT is set at the time a new message is received, it takes precedence and the Courier mail server uses the contents of the environment variable instead. Changes to this file take effect immediately. The SIZELIMIT environment variable is for use by individual mail submission agents. For example, it can be set by the smtpaccess configuration file (see makesmtpaccess(8) for more information) for mail from certain IP addresses.

If sizelimit does not exist, and SIZELIMIT is not set, the maximum message size defaults to 10485760 bytes.

submitdelay specifies the delay before the first delivery attempt for a message that has been entered into the mail queue. Normally, the first delivery attempt is made as soon as possible. This setting delays the initial delivery attempt. It is normally used when you have a mail filter installed that detects duplicate messages arriving in a short period of time. If the mail filter detects this situation it can use the cancelmsg(1) command to reject duplicate messages in the queue (and return them back to the envelope sender).

submitdelay specifies a time interval in the same format as queuetime.

If this configuration file exists, the Courier mail server's webmail server will set the X-Sender: header on all outgoing messages. This is a good idea if the webmail server allows the user to set the contents of the From: header. Note that the Courier mail server records the system userid of the sender in all locally-sent messages (which includes messages mailed by the webmail server), which is sufficient in most cases. In cases where you have many virtual accounts that share the same system userid, this configuration file provides a way to positively identify the sender of the outgoing message.

uucpme sets the UUCP nodename of the Courier mail server mail relay. See courieruucp(8) for more information.

uucpneighbors is used by the courieruucp module to specify the Courier mail server's configuration for relaying mail via UUCP. See courieruucp(8) for more information.

If this file exists, headers of messages sent to/from UUCP addresses will be rewritten. Normally, only the message envelope sender and recipients are rewritten, the existence of this file causes the headers to be rewritten as well.

Enable per-message virtual configuration settings described in the section called “Servers with multiple IP addresses” and the section called “Simulating a server with multiple IP addresses”, below, for more information.

warntime specifies an amount of time in the same format as queuetime. If a message still has not been delivered after this period of time, the Courier mail server sends a warning message (a "delayed" Delivery Status Notification) to the sender. If warntime is missing, the Courier mail server sets warntime to four hours.

When the contents of the me configuration file begin with “*.”, the asterisk gets replaced by the system's hostname. For example:

When a line in these configuration files is “*” or begins with “*.”, the asterisk gets replaced by the system's hostname. For example:

This file consists of a single line of text, which names the character set used by the HTML template files. It is possible to specify multiple character set, by separating them with commas, provided that HTML templates use only the common portions of all listed character set.

The default English HTML templates use strictly the “us-ascii” subset, and the CHARSET contains utf-8,iso-8859-1. When multiple character sets are listed, the first character set that's supported by the browser is picked, so with UTF-8 capable browsers the default webmail interface will use UTF-8, falling back to ISO-8859-1 for browsers that do not support UTF-8.

The contents of this file, if it exists, are appended to all messages sent by the webmail server.

This file consists of a single line of text, which contains the name of the dictionary used for spell-checking. It is passed as an argument to ispell, or aspell.

This file consists of a single line of text, which should always be the same as the name of its directory (en-us).

This file is not needed at runtime, its contents are used during installation. See webmail/html/README_LANG in the source distribution for more information.

The corresponding C locale for these templates.

This file lists the available timezones on the login screen. See the comments in this file for more information.