While Mail Forwarding with exim, how to rewrite the To header with true destination address

exim

I have mail forwarding setup with exim using a domain forwarding file.

virtual_aliases_nostar:
  driver = redirect
  allow_defer
  allow_fail
  data = ${if exists{/etc/valiases/$domain}{${lookup{$local_part@$domain}lsearch{/etc/valiases/$domain}}}}
  file_transport = address_file
  group = mail
  pipe_transport = virtual_address_pipe
  retry_use_local_part
  domains = lsearch;/etc/localdomains
  unseen

It is working fine.

However, I would like to rewrite the "to" header. In my system filter, I would like to put something like:

  headers remove to
  headers add "To: $recipient:"

I've tried:

  headers remove to
  headers add "To: $recipient:"

  headers remove to
  headers add "To: $h_env-to:"

  headers remove to
  headers add "To: $env-to:"

The intent is to have the end recipient see their own email address in the To: line of their mail client.

I can't seem to figure out what the correct header is for the final destination of the email so that I can put it in the to header. I've read through the Exim docs and can't seem to find it. I've also looked in the headers in an email at a mail client and can't see it there either.

Any suggestions would be appreciated.

Best Answer

You want to replace the existing To: header (which may contain other recipients or the name of a mailing list) with the computed final destination of the email? You already have some code to figure out where the email has to end up, so use that:

headers remove to
headers add "To: ${if exists{/etc/valiases/$domain}{${lookup{$local_part@$domain}lsearch{/etc/valiases/$domain}}}}"

Related Solutions

Exim MTA shows dmz address and local domain name in outgoing message headers

The content of the Received: header is defined in Exim by the configuration option received_header_text. The default setting, from which you can see how your example is constructed, is:

received_header_text = Received: \
  ${if def:sender_rcvhost {from $sender_rcvhost\n\t}\
  {${if def:sender_ident \
  {from ${quote_local_part:$sender_ident} }}\
  ${if def:sender_helo_name {(helo=$sender_helo_name)\n\t}}}}\
  by $primary_hostname \
  ${if def:received_protocol {with $received_protocol}} \
  ${if def:tls_cipher {($tls_cipher)\n\t}}\
  (Exim $version_number)\n\t\
  ${if def:sender_address \
  {(envelope-from <$sender_address>)\n\t}}\
  id $message_exim_id\
  ${if def:received_for {\n\tfor $received_for}}

As for changing or remove the header. Beware some best practice advice lies ahead..

Are you sure that you want to remove this information? It's presence allows you to track abuse reports much more easily. The exposure of your internal IP addresses is actually of fairly limited risk.
Technically you can remove this first received header by using headers_remove but it's certainly not RFC friendly and there is a chance of creating mail loops.
If you must mask the information then you would be best to do so by modifying received_header_text. For maintainability and the principle of least surprise, even if the MTA isn't performing any other functions, you probably want to make your changes as specific as possible. This would involve putting some additional conditions in those if statements for facts that you know will always be true, such as whether the sender has authenticated themselves.

Debian – Address rewrite on Exim4 Light not working

Look in /etc/mailname Info in this file can conflict, causing rewrite not to work.

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