Safety Net helps protect against Mailbox server failures in which transaction logs are lost. If a failure occurs and some transaction logs are not replicated to the passive copy, you can use Safety Net to redeliver messages.
Safety Net in Exchange Server 2013 improves the transport dumpster in Exchange Server 2010 in the following ways:
- Safety Net is redundant and uses shadow redundancy to provide a shadow Safety Net queue on another server. Shadow redundancy does not keep another copy of the message, as does the transport dumpster in Exchange Server 2010. If the primary Safety Net is unavailable for more than 12 hours, the resubmit requests become shadow resubmit requests, and messages are redelivered from the shadow Safety Net.
- Safety Net does not require a DAG. It uses the same server that shadow redundancy uses to store a shadowed Safety Net copy.
How Safety Net Works
1. The Transport service on the primary server processes the primary message.
2. The Mailbox Transport service delivers the message to the local mailbox database. Then the message is moved from the queue to the primary Safety Net queue.
3. The shadow server frequently polls the primary server for the discard status of the primary message.
4. After the discard status is received, the shadow server moves the message from the shadow queue to the shadow Safety Net queue.