If the Primary Safety Net is unavailable for more than 12 hours, resubmit requests become shadow resubmit requests, and messages are re-delivered from the Shadow Safety Net. Safety Net itself isn't a single point of failure: Redundancy is provided by using a Primary Safety Net and a Shadow Safety Net. Safety Net doesn't require a DAG: For Mailbox servers that don't belong to a DAG, Safety Net stores copies of the delivered messages on other Mailbox servers in the local Active Directory site. Here's how Safety Net is improved from the transport dumpster in Exchange 2010: You can specify how long Safety Net stores copies of the successfully processed messages before they expire and are automatically deleted. This queue stores copies of messages that were successfully processed by the server. Safety Net is a queue that's associated with the Transport service on a Mailbox server. Here's how Safety Net is similar to the transport dumpster in Exchange 2010: Exchange 2016 and Exchange 2019 have these same improvements. The transport dumpster was improved in Exchange 2013 and is now called Safety Net. When a mailbox database or server failure required the promotion of an out-of-date copy of the mailbox database, the messages in the transport dumpster were automatically resubmitted to the new active copy of the mailbox database.

In Exchange 2010, the transport dumpster helped protect against data loss by maintaining a queue of successfully delivered messages that hadn't replicated to the passive mailbox database copies in the database availability group (DAG).

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