Backups expire based on Data Protection for Exchange policy.
Expiration is the process by which Exchange Server backup objects are identified for deletion when the expiration date is past or the maximum number of backup versions that must be retained is reached.
The data value depends on the business needs that are identified by the recovery point objective (RPO) and the recovery time objective (RTO) of your enterprise. For example, legal, operational, and application requirements affect how data must be protected to meet these RPO and RTO demands. With Data Protection for Exchange, you can specify the number of snapshot backups to retain and the length of time to retain them.
Backups can expire during the query, backup, or restore operation of a Data Protection for Exchange session.
For Exchange Database Availability Group (DAG) backups that use the DAG node, only the system on which the backup is created can cause a local backup to expire. If a new backup is created on a different system, and it exceeds the number of backups to be retained, the oldest backup expires from the Tivoli® Storage Manager server. An expired backup can no longer be restored. However, the physical storage for that backup version is not released until the next time the original system runs a backup, query, or delete operation.
A number of backup copies are retained. When the maximum number of backup copies is reached, the oldest backup expires and is deleted. The maximum number of backup copies is specified in the Data Protection for Exchange policy.
A backup copy is retained for a maximum number of days. The maximum number of days that a backup can be retained is specified in the Data Protection for Exchange policy.