Forward or save outgoing email with Exim

16-12-2015 | Remy van Elst

Table of Contents

I have a specific server where requirements state that all outgoing email should be saved for archival and auditing purposes. The server uses the Exim mail transfer agent, which makes this easy to configure. The outgoing email is also forwarded to an off-site mailbox, both for backup and easy consulting. This captures all outgoing email, sent by PHP scripts or cronjobs, or user accounts that send via exim. This tutorial also shows how to forward or save all outgoing email for a specific domain.

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Exim configuration

There are two things that need to be configured. The system filter and the specific transport. If you only want to forward emails and not save them to the filesystem, the transport section is not needed.

Edit your exim configuration and add these lines at the top:

# /etc/exim.conf top
system_filter = /etc/system_filter.exim
system_filter_directory_transport = local_copy_outgoing

Add these lines lower in the configuration, in your transports section:

# /etc/exim.conf transpors section
  driver = appendfile
  group = mail
  user = mail
  mode = 0660
  maildir_format = true
  create_directory = true

Change the mail user to the specific user account on your system exim runs at. It could be named exim. You can check that with the getent passwd command.

To configure the actual saving and filtering create or edit the /etc/system_filter.exim file. The below snippets should be placed in that file, according to what you're trying to acomplish.

To save all outgoing mail from a specific domain to a maildir folder in /var/mail/:

if $sender_address_domain is example.tld
unseen save /var/mail/example.tld/mailarchive/.${tr{$sender_address}{.}{_}}.outgoing/

Forward all outgoing from specific domain to specific email address:

if $sender_address_domain is example.tld
unseen deliver

Forward ALL outgoing mail to email address:

unseen deliver

Save ALL outgoing email to maildir folder:

unseen save /var/mail/${tr{$sender_address_domain}{.}{_}}/mailarchive/${tr{$sender_address}{.}{_}}.outgoing/

The files are saved in a maildir structure:

ls -la /var/mail/example.tld/mailarchive/example\@example.tld.outgoing/new/
total 16
-rw-rw---- 1 mail mail 1632 Dec 15 20:31 1450207897.H829447P10443.example.tld
drwx------ 5 mail mail 4096 Dec 15 20:31 ..
-rw-rw---- 1 mail mail 1747 Dec 15 20:33 1450207983.H51962P10484.example.tld
drwx------ 2 mail mail 4096 Dec 15 20:33 .

You can check the exim documentation for more variables you can use in this filter document.

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