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Is there any way to perform SRS, or something similar using Postfix?

When I get a mail from user@example.org, I forward it (via a catchall) to something@gmail.com, but GMail is checking SPF, and seeing that my server is not authorized to send mail on behalf of example.org. I'd like to rewrite the sender to something@myserver, while leaving the from as user@example.org.

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3 Answers 3

Here are some thoughts, which will require some customization to meet your exact needs. The first thing I found was that Postfix doesn't seem to like doing anything to addresses that are aliases (i.e. virtual_alias_domain/virtual_alias_maps). But that's fine since in reality it doesn't matter what these addresses are called as long as everything gets delivered properly in the end.

So, in Postfix's main.cf, add the following lines:

virtual_mailbox_domains = example.org
# Feel free to give munger a better name, just update master.cf appropriately
virtual_transport = munger:

Next, you need to tell Postfix what munger actually means. Add the following (see pipe(8) for more options). So add the following to master.cf:

munger    unix  -       n       n       -       -       pipe
  flags= user=nobody argv=/usr/bin/redirector

According to the above, anything destined for example.org will get sent to the /usr/bin/redirector program (or whatever you want to call it). For most normal things, you'd need some command line arguments for sender/recipient information (again, pipe(8) has more details) but since the sender and destination addresses are fixed, nothing else is needed on the command line.

Now you just need to write the redirector program. This worked for me:

/usr/sbin/sendmail -bm -f 'something@myserver' 'something@gmail.com'

It's a regular shell script (or your language of choice) so make it as simple or complex as you like.

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This isn't srs, you can't use it for passing bounces back to the origonal sender securely. –  JasperWallace Sep 9 '13 at 15:38

You would better forget the whole spf thing and use dkim instead.

Here is a good article describing SPF problems.

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Try telling that to Google - as it's Gmail doing the checking not the poster. –  Andy Shellam Feb 25 '10 at 8:26
Google is checking the records that the OP set up. –  cstamas Mar 31 '10 at 23:30
That article was written in 2004, and some of what it says is no longer true; for example, SPF now has its own DNS record type, per RFC4408. Nearly the whole of the rest of the article boils down to "it breaks simple forwarding" and "its arbitrary rewriting of the envelope-from breaks these other systems which arbitrarily use the envelope-from". The former is true, but a price worth paying, to my mind; the latter is true, and tough - one arbitrary use is not implicitly better than another. –  MadHatter Nov 14 '10 at 9:56

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