Did you restart your SMTP VS or your SMTP service when you received these NDRs?
On a Windows Server 2003-based SMTP gateway server, some messages may remain in the queue folder until the SMTP service is restarted
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We had an "incident" on the 12th, where our authoritative DNS (BInd) servers were overwhelmed and unresponsive for part of a day. Our inbound and outbound email was impacted. Just yesterday, the 24th, several users have received NDR's as shown below from messages sent on the 12th. I've verified that the Expiration Timeout on our SMTP virtual servers is set to 2 days, and 12 hours for delay notification.
I'm trying to figure out how/why it took, this long for the messages to die. They were all addressed to valid external recipients, but it can't see any evidence of retries. Due to our volume of mail, we only keep tracking logs for 3 days.
Any insight or even WAG's (Wild Ass Guess) are welcome.
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