We've been plagued by spam recently, and have deployed Exim's sender_
reject and host_reject options at times. However, the current way these
work isn't as useful as it might be. Sender_reject sends a 5xx error
code to MAIL FROM; host_reject (and net_reject) send a 5xx error code at
connection time.
Neither of these actions seem to stop many sending hosts from repeatedly
trying to send the messsage. I believe that 5xx after MAIL FROM should
cause an abandonment (and Exim does this), but the meaning of 5xx on
connection isn't so obvious - and even Exim reacts to it by deferring
and trying again later. Food for thought on that one.
Anyway, I'm implementing new options which will cause Exim to do the
rejection in a different way. Instead of rejecting immediately the
prohibition is discovered, it will carry on until the RCPT TO commands.
At this point, every RCPT TO will be rejected with a 550, the only
version of "no" that some mailers apparently understand.
What I'd like to ask for views on is whether this new style should be
the default or not. It would be an incompatible change, but would affect
only those sites that had set one of the rejection options. I have a
feeling it will be the more useful setting and I would like to make it
the default.
[None of this affects the relay prohibition options, which already do
their rejections at RCPT TO time.]
--
Philip Hazel University Computing Service,
ph10@??? New Museums Site, Cambridge CB2 3QG,
P.Hazel@??? England. Phone: +44 1223 334714
