Mailscanner watermarks and compatibility with other systems

Jonas Akrouh Larsen jonas at
Mon May 26 10:29:27 IST 2008



I think you misunderstand, we do not want to filter at the exchange server,
we only want to tag outgoing mail. So if we stamp outgoing mail on the
exchange server, the mailscanner servers can reject backscatter by checking
for valid watermarks. The backscatter never reaches the exchange servers in
that case.


So we will leave all the filtering to the MS installation, we just enhanve
the options for filtering out mail by giving MS more things to check for. Ie
the watermark.


From: mailscanner-bounces at
[mailto:mailscanner-bounces at] On Behalf Of Koopmann,
Sent: 26. maj 2008 11:14
To: MailScanner discussion
Subject: RE: Mailscanner watermarks and compatibility with other systems


> Obviously some will say ". just send outgoing through MailScanner or
similar system" but for some of us that's simply isn't the smartest/best way
to go about fighting backscatter. So for us the event sink/transport agent
method is brilliant and right on the spot.


Well obviously you have good reasons for doing what you are doing. However
one problem persists: If you discard all the backscatter at the Exchange
level it means you already accepted all the crap on your gateway, scanned it
for spam and viruses and then transport it to your customer. Once you face a
really big backscatter attack you will see that this is a big problem.
Moreover: Please make sure your Exchange plugin does not simply reject the
mail. This would be brilliant in case Exchange received the mail in the
first place but that is not the case in your scenario. If you accept the
mail and then later on Exchange chooses to reject the mail, you might in
turn create backscatter yourself.




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