Update backup-view-edit-policies.md

Add note on possible transient failures if mailbox was just added and not yet setup.

Author: esung22

microsoft-365/backup/backup-view-edit-policies.md

@@ -140,6 +140,8 @@ Follow these steps to set up a backup policy for Exchange mailboxes sites using
 
     > [!NOTE]
     > Adding a mailbox to the backup policy will back up the primary and archive mailboxes.
+    >
+    > Adding a mailbox may temporarily fail if mailbox setup has not had time to complete.  For example, if you recently created the user, licensed the user, or migrated the mailbox from on premises, you may see a transient failure while the mailbox is still being setup. 
 
     ![Screenshot of the Choose selection method page for Exchange.](../media/m365-backup/backup-choose-selection-method-exchange.png)
 
@@ -275,4 +277,4 @@ Follow these steps to view and edit backup policies for Exchange.
 
 Microsoft 365 Backup supports the backup of sites and user accounts from both the central and satellite locations if the multi-geo feature is enabled on your tenant. This means that you can add the sites or user accounts from all geos while creating the backup configuration policy via the CSV file upload method. Adding sites via the site picker, search, or filter rules doesn't currently support multi-geo. Those user interface experiences today only support addition of sites in the tenant's central location.
 
-Most importantly, data in the backups will honor the multi-geo residency requirements and keep data in the geo you've defined it to live.
+Most importantly, data in the backups will honor the multi-geo residency requirements and keep data in the geo you've defined it to live.