20.12.5.1 To Restore Messages from a Mailbox that has Been Incrementally Backed-up

If you are restoring messages from a mailbox that has been incrementally backed-up, and if that mailbox exists on the server on which you wish to restore the messages, then restoring the messages requires a straightforward imesrestore. However, if you wish to restore messages from a mailbox that has been incrementally backed-up, and if that mailbox no longer exists, you must follow different restore procedures.

Use one of the following procedures to restore messages to a mailbox that does not exist on the message store server:

• During the restore operation, disable delivery of messages to the user. Do this by setting the LDAP attribute mailDeliveryOption to hold.

• Before you use imesrestore, create the mailbox with the mboxutil -c command.

The reason why these instructions must be followed for restoring an incremental backup is as follows: When a mailbox has been deleted or is being migrated, the imsrestore utility recreates the mailbox with the mailbox unique identification validity and message unique identifications (UIDs) stored in the backup archive.

In the past, when imsrestore would recreate a deleted or migrated mailbox, it would assign a new UID validity to the mailbox and new UIDs to the messages. In that situation, a client with cached messages would have to resynchronize the mailbox UID validity and message UIDs. The client would have to download the new data again, increasing the workload on the server.

With the new imsrestore behavior, the client cache remains synchronized, and the restore process operates transparently with no negative impact on performance.

If a mailbox exists, imsrestore assigns new UIDs to the restored messages so that the new UIDs remain consistent with the UIDs already assigned to existing messages. To ensure UID consistency, imsrestore locks the mailbox during the restore operation. However, because imsrestore now uses the mailbox UID validity and message UIDs from the backup archive instead of assigning new UID values, UIDs could become inconsistent if you perform incremental backups and restores.

If you perform incremental backups with the -d date option of the imsbackup utility, you might have to invoke imsrestore multiple times to complete the restore operation. If incremental backups were performed, you must restore the latest full backup and all subsequent incremental backups.

New messages can be delivered to the mailbox between the restore operations, but in this case, the message UIDs can become inconsistent. To prevent inconsistency in the UIDs, you need to take one of the actions describe above.