On Tue, Aug 31, 2010 at 05:07:10PM +0200, Stefan Seidel wrote:
> 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:
> hijac...@yahoo.example.com sends email to u...@mysystem.com ->
> virtual_alias_maps says: deliver it to interestedpa...@gmx.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 hijac...@yahoo.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?
You can't, some backscatter is unavoidable. If the volume is too high
for a given mailbox, you may need to ask the user to stop forwarding
mail via your site. Postfix is not psychic and cannot predict which
mail remote mailbox services will refuse. It would be wrong for Postfix
to silently discard undeliverable mail without sending a bounce.
--
Viktor.
