Exim configuration & Filter

 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

local_copy_outgoing:

  driver = appendfile

  delivery_date_add

  envelope_to_add

  return_path_add

  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

then

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

endif

Forward all outgoing from specific domain to specific email address:

if $sender_address_domain is example.tld

then

unseen deliver othermailbox@otherdomain.com

endif

Forward ALL outgoing mail to email address:

unseen deliver othermailbox@otherdomain.com

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 .

Ref: Exim Documentation