The normal way to block this type of spam is to implement SPF (http://www.openspf.org) and specify the mail servers which are permitted to send mail from your domain. Then configure your mail server to use SPF so any mail from your domain which does not match SPF or is trusted (local users) is rejected.
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by: nociPosted on 2009-01-09 at 14:26:33ID: 23340918
Well this is quite hard except for adding your own domain on the sender blacklist (that would mean that outgoing spam should not be sent through this config).
You don't tell exact what other measures you use.
Do you use greylisting (rejecting the first attempt, accepting a mail only if the 2nd attempt is after 30 minutes or so).
Do you allready use Blacklisting?
Also spamassassin has a ruleset that is updated regularly to adjust for new kinds of spam (sa-update).
Scanners like vipuls razor can help, that react to many mails looking alike to many targets that also use this razor.