The Symantec Messaging Gateway (SMG) will queue messages in the delivery queue for upwards of five days in the event that it cannot reach the destination mail server. While the destination servers are unavailable, queued messages will generate a delivery status notification addressed to the sender every four hours while the message is queued. Delivery attempts are initially made at fifteen minutes with an exponentially decreasing backoff. Once connectivity is reestablished, queued messages will be delivered to the destination mail server.

Minimum retry interval for queued messages: 15 minutes
Maximum queue lifetime: 5 days
Delay notification frequency: 4 hours
Maximum bounce message lifetime: 1 day