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We host websites & email services for youth sports organizations. So in our environment we have a lot of folks who use the aliases to route incoming email to addresses on outside domains - for example "firstname.lastname@example.org" forwards to "email@example.com". Without getting into a philosophical debate about whether doing that is good or bad, for youth sports organizations it's certainly useful.
SmarterMail's spam checking will look at incoming messages that don't have internal recipients like the above and skip spam checks. This makes emails sent to aliases a bit like an open relay, so we've decided to enable spam checking on outgoing mail as well in order to prevent spam sent to an alias from leaving SmarterMail.
All that works, however, it creates a new problem for us in that it clogs up our Spool with undeliverables because the spammer isn't using a valid email address in the first place. For example:
firstname.lastname@example.org -> email@example.com -> firstname.lastname@example.org -> SmarterMail marks as Spam -> Delivery Failure sent to email@example.com
In that last step, because firstname.lastname@example.org doesn't receive incoming mail (and probably isn't a legitimate mailbox), our SmarterMail server puts the Delivery Failure message into the spool and keeps on trying to re-send it per our retry intervals. So it sits in our spool for a few days in a "Waiting To Deliver" status.
So at any given time our spool is 98% (or higher) filled with the Delivery Failure messages.
Is there any event or filter than can be setup somewhere to shorten the number of retries when the subject of the message is "Delivery Failure" and the content of the message contains "This message cannot be delivered as it was marked as spam"? Or should we be doing things completely differently?
Thanks in advance for any suggestions.