Understanding the Safety Net feature in Exchange 2013

Safety net is a new feature of Exchange 2013, comparable to a depreciated feature in earlier versions called "Transport dumpster". They both retain successful messages that have been delivered to a mailbox by the transport service on the Mailbox server and you can also specify the retention period of these stored emails.

Although the Safety Net is not required to be part of a DAG unlike the Transport Dumpster and can simply store copies of the messages on the local Mailbox server of the domain. And it also provides redundancy by means that there are two servers - the Primary Safety Net and the Shadow Safety Net. If mail re-submits are requests are not answered within 12 hours (by default) the Shadow Safety Net is queried instead.

This feature is useful in the event that a mailbox server goes down and has incomplete or corrupt messages in its database, by querying another mailbox server with the Safety Net enabled it can recover its database.