> Apologies if this is a trivial question, I haven't seen it discussed.
> Searching brought up 1 related issue, which 1) was not answered and 2)
> was looking at the problem from the wrong side. This was someone
> wondering how to exclude bounces from the rest that he relayed to his
> I'm at the other side of the problem. We've got a server that's
> relayhost for lots of clients of various configurations and sizes. Some
> of these clients are, in fact, MX-es directly connected to the net, but
> still use our server as an outgoing relay. Those of them that do delayed
> bounces, send their backscatter to us. Supposing that we have to relay
> for them and we can't force them all to stop bouncing, what would be the
> best solution?
> Somehow I don't think that rejecting the null sender is entirely correct.
you can refuse relay if the sender is null (use a map that returns
reject_unauth_destination if the sender is null or mailer-daemon ...).
This will however block legitimate bounces (out of quota, ...). but it
may be better than backscatter...
you can also use a proxy_filter that checks the content of the bounce
and only blocks it if it contains some patterns ("user unknown", "action
not taken", ... etc).