I currently have two files set up - banned_sites (used by
sender_host_reject_recipients) and banned_addresses (used by sender_reject)
which have the (desirable) effect of blocking mail from hosts that don't
have a reverse DNS entry, which was our policy when running XT-PP before
switching to Exim. There have been quite a few occasions recently where
users at UCE have complained that they've been unable to receive mail from
outside and, after investigation, it's turned out to be because the sending
host does not have a reverse DNS entry.
Is there a way of, when rejecting such messages, sending an auto-reply along
the lines of "Sorry, but we are unable to deliver your message because it is
being sent from an un-recognised IP address. Please contact your Service
Provider" ? If so, it might wake a few places up to the fact that
legitimate MTAs should really have reverse DNS entries if they wish to
maximise their delivery potential.
It'd be even better if there were some mechanism whereby the recipient could
be sent a message from Postmaster (or whoever) informing them that a message
from "sender at IP address" was rejected and explaining why. I've found
from experience that trying to explain DNS/reverse-DNS lookups to users is
not exactly easy - even when I've tried to make it analogous to Caller
ID/Caller Display on telephones.
Paul Walsh
Senior Systems Programmer, Information Services,
University of Central England, BIRMINGHAM B42 2SU, UK
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