How to configure postfix to force From: field but leave Reply-To: alone

emailpostfix

I need to configure postfix on a localhost as a relay to an smtp server.
This external smtp server requires From: header to be consistent with the authenticated user name.
I want to fixup the From: header for all the messages originating on this local machine to say authenticated@example.com

I tried the following:

sender_canonical_maps
The problem is: it seems to be overwriting the Reply-To: header as well, I don't need this, on the contrary, I want to use it extensively.

How I checked this:

Put sender_canonical_maps = regexp:/etc/postfix/sender_canonical in main.cf
REPLYTO="some.addr@gmail.com" mail my_addr@gmail.com
Actual results: received message has overwritten Reply-To to authenticated@example.com

Vs:

Remove sender_canonical_maps from main.cf
REPLYTO="some.addr@gmail.com" mail -r authenticated@example.com my_addr@gmail.com
Actual results: received message has correct Reply-To

The problem is this doesn't work without -r authenticated@example.com.

header_checks: apparently doesn't work for From: fields (http://www.postfix.org/header_checks.5.html see Bugs: section)

How can I simply force the From: header on all outgoing mail, but leave Reply-To: alone for local users to specify?

Best Answer

Forcing the from address when postfix relays over smtp

/etc/postfix/main.cf:

smtp_header_checks = regexp:/etc/postfix/header_check

/etc/postfix/header_check:

/From:.*/ REPLACE From: newsender@address.com

Tested with:

mail -s test -a 'Reply-To: a@domain.tld' me@me.com <<< test

Header on client side:

From: newsender@address.com
Reply-To: a@domain.tld
To: <me@me.com>

In syslog you then see

Nov  1 17:20:50 huuu postfix/smtp[4716]: 1B65481FAB18: replace: header From: root@huuu (root): From: newsender@address.com

Related Solutions

How to limit the From header to match MAIL FROM in postfix

If You want to do re-write mail headers, you'll have to have postfix pass the mail through some program which does the re-writing. Have a look at documentation for something like policyd for how that interaction works.

However, I'm not convinced that what you're describing is a good idea, or helpful with spam. If you can't rely on the behaviour of authenticated users, then you need to do content filtering much as you'd do for mail coming in for mail from unknown sources coming to your users.

Mailscanner & Postfix: HOLD everything except messages with a custom header

Yes there is even a solution. It is called header_checks and is part of the *_restrictions. The format (dependent on what you want) is described at it's own documentation.

But I can't recommend using after-queue-filters like Mailscanner and Spamassassin. The better way to reduce Spam and inform the sender are before-queue-filters like the built-in postscreen, client_restrictions, sender_restrictions, recipient_restrictions, before-queue milters and external tools like policyd-weight.

Only before-queue-filters reduce the load and resources on the server and can block 80% of all Spam before they even reach the server. Mailscanner in particular is on my personal "hate-list" as it only has a crippled integration into Postfix and is not able to use Postfix' built-in interfaces for anti-spam filters and filters in general.

Edit: Due to the edited question, I will answer that now.

FILTER is not an action that stops Postfix from working on the header_checks-file. It only tells "when I'm finished with the checks I'll filter". And so the next line matches and sets the mail on hold.

The solution (even if it looks crippled) is this header_checks-file:

/^X-Custom-Header:/ FILTER smtp:[ip.addr.next.hop]:10025
/^X-Custom-Header:/ OK
/^Received:/ HOLD

Best Answer

Related Solutions

How to limit the From header to match MAIL FROM in postfix

Mailscanner & Postfix: HOLD everything except messages with a custom header

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