> I thought those characters looked like Base64...and it turns out, 
> they are. I was able to extract enough from them to figure out the
> account.

only if the session is using the "AUTH login" mechanism (and btw
this means that the server allows such an /unsafe/ option); for more
details, see

http://www.fehcom.de/qmail/smtpauth.html

notice that it may be advisable to use MD5 instead of login/plain
since both are easily "crackable" in case the traffic is sniffed or
in any case intercepted

About finding out which account got compromised, the best way
to do so is to find out the date/time from the ASSP logs and then
look at the mailserver logs; there you'll find the logon infos "in
clear" and those will allow you to track the account

As for tracking such issues (and others) I'd suggest you to use
the "outbound rate limiter" option; expand the "relaying" section
in ASSP GUI and scroll down, you'll find the entries named
"LocalFrequencyInt" and "LocalFrequencyNumRcpt" for a start
set them to 1800 and 120, that means that if a given sender
will go over the imposed "outbound email" limit ASSP will reject
the message with an error (retry after...); now, to get a notify for
such an event, Locate the "notifyRe" under the "Logging"
section and add either "warning: too many recipients" or
"notification: too many recipients" the first one will notify you
about any and each violation, the second will notify you only
once a day about each violation; for a start I'd suggest you
to use the first one (warning) so that you'll immediately get
back messages, at that point, if the sender is a "legit" one
(e.g. a mailing list or a newsletter), just add the sender
address to "NoLocalFrequency" (use a file for that); once
you'll have your "NoLocalFrequency" set up, you may
change the notification regexp to "notification" so that you
will only get ONE alert a day for each sender violating the
rate limiter; btw you may also need to fine tune the limiter
values (1800/120) to better suit your setup, the ones above
are just a starting point

The above mechanism will allow you to detect spamming
users and compromised accounts and quickly act so that
your mail service won't keep *sending* out "junk"



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