When an external user emails someone in my exchange server. An NDR or DSN is created if the total size of email/attachment exceeds the limit. We don't permit postmaster messages to escape our system and return to sender. BUT, how can I alert the recipient in my exchange that this happened? Currently neither the sender or the receiver knows that the message was dropped because of too-large email size. How can i get some automatic notification that this happened? BTW,I'm usind Exchange Server 2010.
You'll want to use the Set-TransportConfig cmdlet to set the GenerateCopyOfDSNFor value for any DSNs you want to monitor (some are there by default), and Set-OrganizationConfig MicrosoftExchangeRecipientReplyRecipient value to a mailbox that should receive Exchange messages (discarded by default/not set).
See Set-TransportConfig: http://technet.microsoft.com/en-us/library/bb124151(v=exchg.141).aspx
See Set-OrganizationConfig: http://technet.microsoft.com/en-us/library/aa997443(v=exchg.141).aspx
Here's a guide that goes over the process for 2007, which is similar: http://technet.microsoft.com/en-us/library/bb400930(v=exchg.80).aspx