Quick question guys:
3 Exchange servers
1 front end webmail (only webmail server, no mailboxes, physically located in site A)
1 backend mailbox server (mailboxes for site A)
1 backend mailbox server (mailboxes for site B)
2 postfix border mail servers (smart hosts, relays... etc.)
Domain controllers at both sites and both sites are connected via a permanent VPN.
Point of entry for ALL email is via site A (MX records pointing to IP's at site A) AND is controlled by two border Postfix servers there.
These smart hosts relay the mail down to the exchange server at site A which distributes accordingly.
Site B will be down for about 4 hours for a move which means email destined for site B will come to the border servers as usual.
I am guessing these will be passed to the exchange server in site A as usual, but my concern is what happens next?
Does the email get deleted as site A cannot communicate with site B's mailbox server? Does it get queued? Does it generate a NDR for the sender? Obviously my preferred outcome is it all gets queued on site A's mailbox server but what really happens?