netcat wrote:
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
relayhost.
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).
