An email bounces back to the sender as undeliverable. The Message Audit Log (MAL) in Symantec Messaging Gateway (SMG) display the status "554 5.4.7 [internal] exceeded max time without delivery".
Log Sample:
2018 Jan 25 10:22:48 CET (info) ecelerity: [31471] ML-PERMFAIL: Message ID: 4B/28-55573-2F27B5B4, Audit ID 50bbc0e0a-b7cbdae000007ed9-6d-4b5b72f14805, Permanent delivery failure, sender: [email protected], Detail: 554 5.4.7 [internal] exceeded max time without delivery
Undeliverable messages are queued and redelivery is attempted up to 5 days. Undeliverable mail after this period is rejected from the queue, and a notification is sent to the sender.
CAUTION: The default value for how long undeliverable messages are queued is an industry best practice. Symantec does not recommend modifying this value unless absolutely necessary.
If the message destination is the Messaging Gateway quarantine, it may indicate an issue with the quarantine. See the following article for more information: