email address probes

[Andy Bastien <lists+incidents () yuggoth net>]

Where I work, we've getting lots of attempts to send email to random
addresses at our domain.  All of these attempts have been coming from
valid servers operated by AOL, MSN, and Hotmail.  I'm guessing that
this is an attempt to find some spam targets, although I suppose that
there could be something worse in store.

I'd like to be able to stop these attempts, but I can't think of a way
to do it.  All of the attempts are coming from valid servers from some
domains that we can't block.  They do all have null reverse-paths
(MAIL FROM:<>), but I don't think that we can reject on this criteria
as null reverse-paths are used to send NDRs and other notifications
which we don't want to block.  I suppose that we could accept the
emails and dump them to /dev/null (or to some tarpit account so that
we can inspect them) instead of replying with a "550 User unknown,"
but I suspect that this could cause us more headaches in the future.
Does anyone have any suggestions as to how we could handle this
problem?




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