Hello everyone,
Opened a case with support, but wanted to hear your opinions on the matter as well:
We recently enabled and redirected all emails for a few of our domains via our UTM. We discovered a strange issue.
We have about 1300 users hosted on an Exchange 2010 server. The Exchange server uses the UTM as a smarthost for delivery. Now, in one particular case, a user (which is not the only one with this set up), has an inbox rule to forward all messages to an external address. What happened with the UTM, is that the external address did not exist so:
1) Exchange would try to forward original message to external address
2) UTM would accept it, but not generate a proper SMTP bounceback.
3) UTM sent it's own bounceback email
4) Message would be delivered back to Exchange and according to inbox rule, message would be attempted to be forwarded again to external recipient
So essentially, we ended up with an SMTP storm. We never had this issue with our fortimail unit. Obviously Exchange treats message delivery failed notifications differently and inbox rules do not apply to them, so why is the UTM sending it's own delivery notification failures?
Thank you,
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