What is the elapsed time for which the Cisco Email Security Appliance reports outgoing domains?
For any outgoing domain with a message waiting to be delivered, the ESA creates a destination object in memory. After all of the messages for that domain have been delivered, the destination object is retained for three hours. If no new messages are bound for the domain after three hours, the object is expired and the domain will no longer be reported in the Outgoing Mail Overview page (or CLI: tophosts command).
You can also check the delivery status on GUI:Monitor -> Delivery Status, or CLI: hoststatus command.
The status of the host will go to unknown after the three hours.