Let's say mail to a recipient flows in this manner:
Exchange 1 > MTA1 > MTA2 > Exchange2
For some reason, Exchange2 is down, and it is down for all of MTA2's retry period.
What happens to the actual message? I know MTA2 sends an NDR back to the address in the return-path, however - say there was a 10MB attachment with the mail, where does this actually go?
My assumption was that it would go the Badmail directory on MTA2...does it ever get deleted from there? Do SMTP servers like Exchange and IIS SMTP have defaults for deleting messages from the badmail queue, otherwise surely it would get so large eventually and fill the drive?