From: Stefan Seidel (postfixstefanseidel.info)
Date: Tue Aug 31 2010 - 10:07:10 CDT

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Hi,

I am using Postfix for some time now and up to now I could always make it
behave the way it should. However, I have a problem now:

I use virtual_alias_maps (with mysql backend, not that it would matter) to
sort mail into local user's mailboxes, but also sometimes to forward mail
to external mail addresses (upon user request). I know that this kind of
forwarding is not always the best, but it works most of the time.

This forwarding to external addresses however, makes my Postfix create
backscatter. Example:
hijackedyahoo.example.com sends email to usermysystem.com ->
virtual_alias_maps says: deliver it to interestedpartygmx.example.com
However, the mail server at gmx.example.com may sometimes reject the
message for any reason, which causes my Postfix to generate a bounce
message to hijackedyahoo.example.com - which is obviously not something
anyone would want.

Any proposed solutions I found always attacked the problem either using
spam filters (not applicable in this case) or changes in the receiving mail
server (how would I convince any bigger email provider to do that?).

The backscatter FAQ about Postfix gives loads of things to do for
preventing incoming backscatter, but now Postfix is generating the
backscatter. How do I stop it from doing so?

Thanks,

Stefan

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