After Directory Synchronization completes and users are then added to Mail or Calendar Synchronization collections, which are configured to move the mailboxes to a different Mailbox Database other than where the Directory Synchronization Agent created the "stub" mailbox. The following error will be present in the MAgE log:
2015-01-15 21:08:07.7925 Px4024 Tx17 A21 C8 M4 Trace Execute PowerShell: New-MoveRequest -Identity e0d688f4-dcc2-4c83-9b20-577b2d5e0021 -TargetDatabase c9c202a9-2fed-4dee-8a3b-d1282daf6d0b -BatchName QMMEX(2BB01037-E212-4872-8363-D15DB47FF6A3), TargetDB(c9c202a9-2fed-4dee-8a3b-d1282daf6d0b) -BadItemLimit Unlimited -AcceptLargeDataLoss
2015-01-15 21:08:07.8393 Px4024 Tx17 A21 C8 M4 Trace PowerShell command executed 2015-01-15 21:08:07.8393 Px4024 Tx17 A21 C8 M4 Warning When an item can't be read from the source database or it can't be written to the destination database, it will be considered corrupted. By specifying a non-zero BadItemLimit, you are requesting Exchange not copy such items to the destination mailbox. At move completion, these corrupted items will not be available at the destination mailbox.
2015-01-15 21:08:07.8393 Px4024 Tx17 A21 C8 M4 Error System.Management.Automation.RemoteException: The operation couldn't be performed because object 'e0d688f4-dcc2-4c83-9b20-577b2d5e0021' couldn't be found on 'DC.DOMAIN.COM'.
Calendar Synchronization and Mail Synchronization for users not moving between Mailbox Databases works without issue.
More on the cause of this issue can be found in the following Microsoft Knowledge Base article: