Alex Moore wrote:
How can I setup a rule in MIMEDefang to define those transactions?  Say
when a smtp server tries 10 times within a short time period and is sent
a 550 code each time. I think that it would appropriate to have MD just
blacklist that address. Is that possible?  I want to ignore them
completely after this event has occurred.

Well, this isn't MIMEDefang, but we've had good luck with a variation on the rumplekiller script (some people refer to dictionary attacks as "Rumplestiltskin attacks") here:
http://bignosebird.com/notebook/rumplekill.shtml

The script runs from a cron job and checks the mail logs for excessive "User unknown" hits from an IP address. The original version uses IP routing commands to ignore all incoming connections, but it's easy enough to adapt it to other actions (we have it add the IP to our local blacklist, for instance).

You might also look into Sendmail's BAD_RCPT_THROTTLE feature. It doesn't block them, but it'll slow them down a bit.

--
Kelson Vibber
SpeedGate Communications <www.speed.net>
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