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       dot-courier - Local mail delivery instructions






       In most cases delivering mail to an account means simply placing the
       message in the account´s system mailbox, but that does not have to be
       the case. Alternate mail delivery instructions include running a
       separate program to process the message, or forwarding the message to
       another address. The various .courier files specify some basic mail
       delivery instructions. If sophisticated mail filtering is required, the
       delivery instructions should include running an external mail filter,
       such as maildrop(1)[1].

       The file $HOME/.courier specifies how messages are delivered to this
       account. If this file does not exist, default instructions set by the
       system administrator are used. The system administrator´s default
       instructions specify the location of the account´s system mailbox.

       In addition to receiving mail addressed user@domain, it is also
       possible for user to receive mail addressed to user-foo@domain, for
       arbitrary values of foo. To do this, install $HOME/.courier-foo, with
       delivery instructions for mail addressed to user-foo@domain.

       The system administrator can configure the Courier mail server to
       accept mail without regard to whether addresses are in uppercase and
       lowercase. In that case the name of a .courier file must contain only
       lowercase characters. In any event, all periods in the address must be
       replaced with colons. For example, to specify delivery instructions for
       user-Foo.Bar@domain, put the delivery instructions in

       The file $HOME/.courier-foo-default specifies delivery instructions for
       any user-foo-bar@domain address, where bar can be anything. However, it
       does NOT control mail delivery to user-foo@domain, which is controlled
       by $HOME/.courier-foo.

       Possible mail delivery instructions include: whether each message
       should be delivered to a non-standard mailbox; forwarded to another
       E-mail address; or if another program should be executed to handle the
       message. Programs executed from a .courier file have access to some
       environment variables (see ENVIRONMENT VARIABLES). Programs executed
       from a -default file can read those environment variables to determine
       the exact E-mail address the message was delivered to.

   Default delivery instructions
       The /etc/courier/aliasdir directory is searched as the last resort,
       when all attempts to figure out how to deliver mail to a local address
       have failed.

       /etc/courier/aliasdir´s functionality is very similar to how the alias
       account is implemented in Qmail, except that no actual system account
       is needed. If <> is a local address, and there is no
       such system account, nor is there an alias defined for this address,
       the Courier mail server attempts to read delivery instructions from

       All the usual aspects of .courier deliveries apply. If there is no
       account that corresponds to the address <>, the
       Courier mail server looks for /etc/courier/aliasdir/.courier-user-foo,
       then /etc/courier/aliasdir/.courier-user-default, and finally

       It therefore follows that you can use
       /etc/courier/aliasdir/.courier-default to specify local mail delivery
       instructions for addresses that do not exist. Combined with dynamic
       mail delivery instructions (see below), that´s one way to specify
       non-standard locations of mailboxes.

   Program/mailbox aliases
       The directory /etc/courier/aliasdir/.courier-:xalias/ is created and
       maintained by the makealiases(8)[2] script to implement aliases that
       deliver directly to programs or mailboxes. See makealiases(8)[2] for
       more information. (This directory corresponds to local addresses that
       begin with ".xalias/", but the Courier mail server prohibits explicit
       local addresses that begin with a period).

       Additionally, makealiases(8)[2] creates subdirectories named
       /etc/courier/aliasdir/.courier-:xalias-protocol/, where "protocol" is
       set by the -m option.

       Each .courier file specifies zero or more delivery instructions. If the
       .courier file is zero bytes long, it means that default mail delivery
       instructions set by the system administrator should be used. If the
       file is not a zero length file, and does not specify any delivery
       instructions, messages to the corresponding E-mail address are silently

           If $HOME/.courier does not exist, it is treated as a zero-length
           file, resulting in a delivery to a default mailbox. If
           $HOME/.courier-foo does not exist, it is treated as a non-existent
           address, returning the message as undeliverable.

       If home directories have global read and execute permissions, the
       Courier mail server will be able to reject mail to non-existent
       mailboxes right away. the Courier mail server´s ESMTP server runs as a
       non-privileged process. It will not be able to access home directories
       which do not have global read and execute permissions. Therefore, the
       message will be accepted for delivery, by the Courier mail server. As
       soon as an attempt to deliver the message is made, the missing .courier
       file will result in the message being returned as undeliverable.
       However, here the Courier mail server has to accept the message for
       delivery first, before generating a non-delivery report.

       Delivery instructions in .courier are executed one at a time. If the
       execution of a delivery instruction fails for some reason, the message
       is either returned as undeliverable, or requeued for another delivery
       attempt. Messages that remain queued for a long period of time are
       returned as undeliverable.

           Even if one delivery instruction fails (and the message is returned
           as undeliverable) previous delivery instructions in the file will
           have been completed anyway.

       Blank lines in the file are ignored. Lines starting with the #
       character are comments, and are also ignored. Otherwise, each line
       specifies one of three possible delivery instructions: deliver to a
       system mailbox or a Maildir; run an external program; or forward the
       message to another address.

       Lines that start with the .  or the / character specify a mailbox or a
       Maildir delivery. The line must specify the complete location of the
       mailbox file, or a Maildir. Filenames starting with .  are relative to
       the account´s home directory. A mailbox file is a traditional mailbox
       file that´s readable by most mail software. A Maildir is a directory
       based mail storage format that offers several advantages over mailbox
       files. Mailbox files must be locked, and therefore they do not permit
       concurrent mail deliveries. The mailbox file must be locked while a new
       message is appended to it, otherwise multiple messages being delivered
       at the same time will trample all over each other. Maildirs do not
       require locking, and multiple concurrent deliveries can be made to the
       same Maildir. You can create Maildirs by using the maildirmake(1)[3]

           The Courier mail server does not implement the "dot-locking" form
           of mailbox file locking. The Courier mail server´s locking
           abilities are limited solely to system file locking facilities
           (namely the lockf, or flock system calls). You can always use
           maildrop(1)[1], which offers additional locking options.

       Lines that begin with a single | character run an external program. The
       rest of the line specifies the command to be executed by the shell.
       Long commands can be continued on another line by terminating the
       previous line with the \ character.

       The Courier mail server runs the specified command, and provides the
       contents of the message on standard input.

       The Courier mail server waits until the external command completes
       execution before going to the next delivery instruction. The Courier
       mail server examines the exit code of the external command in order to
       determine whether the delivery failed, or not.

       If the external command terminates with the exit code of zero, the next
       delivery instruction is executed. If the command was the last delivery
       instruction in the file, the message is considered to be successfully

       If the external command terminates with the exit code of 99, any
       additional delivery instructions in the file are NOT executed, but the
       message is considered to be successfully delivered.

       If the external command terminates with any of the following exit
       codes: 64, 65, 67, 68, 69, 70, 76, 77, 78, 100, or 112, the E-mail
       message will be returned as undeliverable, and no further delivery
       instructions will take place.

       If the external command terminates with any other exit code, it is
       interpreted as a temporary error, and the message will be requeued for
       another delivery attempt later.

           On subsequent delivery attempts, delivery instructions will be
           carried out from the beginning of the .courier file.

       Lines that begin with the || characters also run an external program.
       The rest of the line specifies the command to be executed by the shell.
       Long commands can be continued on another line by terminating the
       previous line with the \ character.

       However, programs that are executed by the || instruction, unlike |,
       have their standard output captured, and reinterpreted as additional
       delivery instructions to be carried out. This feature allows an
       external program to be invoked to generate dynamic delivery
       instructions to be carried out by the Courier mail server.

       The standard output of the external program is read and parsed as if it
       contained .courier delivery instructions. There´s a fixed upper limit
       on the number of bytes in dynamically-generated delivery instructions.
       For glibc, the limit is 8191 bytes, other systems´s upper limit should
       be similar.

       The dynamically generated delivery instructions may also specify ||
       instructions, recursively. There is an upper limit of four recursive
       dynamically-generated delivery instructions.

       The exit code of the program invoked by the || instructions are
       interpreted exactly like the exit code of a program invoked by |, with
       the following exceptions. Dynamically-generated delivery instructions
       are carried out only if the external program terminates with an exit
       code of 0 or 99. Any other exit code discards any dynamically-generated
       delivery instructions. All other aspects of exit code treatment of
       external programs remains the same. If the exit code is 99, the
       delivery is deemed to be successful, and any additional instructions in
       the original .courier file are ignored. If the exit code is 0, the
       remaining instructions in the original .courier file are executed.

   Alias-based deliveries
       When the Courier mail server delivers to default delivery instructions
       in /etc/courier/aliasdir, those delivery instructions are carried out
       under the Courier mail server´s installed system user and group id.
       That means that any executed programs or mailboxes are accessed as the
       Courier mail server´s mail system user and group.

       External commands executed from the .courier file will have the
       following environment variables:

           The home directory.

           The recipient´s userid.

           The message envelope return address.

           The complete receipient address.

           When RECIPIENT is of the form user@domain, HOST contains the domain
           part of the address.

           When RECIPIENT is of the form user@domain, LOCAL contains the user
           part of the address.

           When USER is of the form $USER-foobar, EXT will contain the foobar

           The portion of EXT that follows the first dash.

           The portion of EXT2 that follows the first dash.

           The portion of EXT3 that follows the first dash.

           When delivery instructions for the address user-foo-bar@domain come
           from the file $HOME/.courier-foo-default, DEFAULT will contain the
           bar part.

           This environment variable contains the entire From_ header that
           should be prepended to the message if it is to be delivered to a

           This environment variable contains the entire Return-Path: header.

           This environment variable contains the entire Delivered-To: header.

           When the external program reads the message from standard input,
           the message will NOT have the customary From_, Return-Path:, and
           Delivered-To: headers which are customary for locally-delivered
           messages. The external program can find those headers in the
           respective environment variables. If you have a command that
           expects to see those headers as a part of the message, you can use
           the preline(1)[4] wrapper to add them to the message. For example,
           the procmail mail filter requires those headers.

           The maildrop mail filter will not require preline if the system
           administrator correctly configures the Courier mail server. The
           system administrator can optionally configure the Courier mail
           server to recognize maildrop, and activate certain
           maildrop-specific optimizations in the Courier mail server. If
           these arrangemenets have been made, you can run maildrop directly
           from the .courier file, in a straightforward fashion, but those
           headers will automatically appear in the message, as seen by
           maildrop. Because the message is provided directly on standard
           input, without using a pipe, maildrop will be able to deliver the
           message directly from the Courier mail server´s message queue,
           without using a temporary file.

       Lines that do not start with the ., /, or the | character specify a
       comma-separated list of E-mail addresses to forward the message to. If
       the line starts with either the & or the !  character, the character is
       ignored; this is a legacy compatibility option.


       The Courier mail server´s .courier may seem to be exactly like Qmail´s
       .qmail, but there are some minor differences. Qmail, as of 1.03, does
       not implement dynamic delivery instructions. The Courier mail server
       also uses a slightly different set of return codes which are classified
       as hard errors. The Courier mail server´s implementation of forwarding
       differs from Qmail´s. According to Qmail´s documentation, if any
       external command terminates in a permanent or temporary failure, the
       message is not forwarded to any forwarding address in the .qmail file,
       even to addresses that precede the failed delivery instruction. The
       message is forwarded only after it is successfully delivered. The
       Courier mail server forwards messages to addresses immediately. Also,
       in some cases Qmail resets the return address on the message to the
       address of the account being forwarded.

       To make things more confusing, there is a configuration setting to have
       the Courier mail server read $HOME/.qmail files, instead of


       dot-forward(1)[5], maildirmake(1)[3], maildrop(1)[1], courier(8)[6].


        1. maildrop(1)
           [set $man.base.url.for.relative.links]/maildrop.html

        2. makealiases(8)
           [set $man.base.url.for.relative.links]/makealiases.html

        3. maildirmake(1)
           [set $man.base.url.for.relative.links]/maildirmake.html

        4. preline(1)
           [set $man.base.url.for.relative.links]/preline.html

        5. dot-forward(1)
           [set $man.base.url.for.relative.links]/dot-forward.html

        6. courier(8)
           [set $man.base.url.for.relative.links]/courier.html