The MessageExpirationTimeout parameter of Microsoft Exchange Server specifies the maximum time that a particular message can remain in the queue. If a message remains in the queue for longer than the value defined in MessageExpirationTimeout, the message will be returned to the sender as a permanent failure.
The default value of MessageExpirationTimeout is 2 days. This means that if an email spends more than 2 days in Quarantine or in Audit > Email History then releasing or forwarding and retrying (accordingly) after 2 days will fail.
The maximum value MessageExpirationTimeout can be extended is 90 days.
For further details see 3.10 Onsite Microsoft Exchange deployment.
This article pertains to
Email Security v4.0.0 or above
This article was last updated on 2018-03-28