Due to limitations and functional issues with (Messaging Application Programming Interface) MAPI backup mode, which is a Microsoft technology used by Ahsay to enable MS Exchange Server 2013 mail level backup and restores, starting from Microsoft Exchange 2013 Cumulative Update 23 or above MAPI backup mode may stop working. To avoid issues with Microsoft Exchange 2013 mail level backup and restores, it is strongly recommend to transition from MAPI backup mode to (Exchange Web Services) EWS backup mode as soon as possible.

If you continue to use MAPI backup mode and MS Exchange Server 2013 is updated to Cumulative Update 23 or above. This will result in the following outcome:

• MS Exchange 2013 mail level MAPI backup jobs will stop working.
• All mailbox items already backed using MAPI will no longer be recoverable to a MS Exchange 2013 database.

Furthermore, MAPI backup mode is not fully functional after MS Exchange Server 2013 Cumulative Update 20 or above is applied, as MAPI is unable access Public Folder items from the MS Exchange 2013 database. This will result in the following outcome:

• Inability to backup items in the MS Exchange 2013 Public Folder databases.
• Inability to restore items to the MS Exchange 2013 Public Folder databases.

Please note after installation of the cumulative update 23 package, you cannot simply uninstall the package to revert to an earlier version of Exchange Server 2013. If you try to uninstall this cumulative update package, the entire Exchange Server 2013 installation will be removed from the server. https://support.microsoft.com/en-hk/help/4489622/cumulative-update-23-for-exchange-server-2013

This issue only affects clients currently running MS Exchange mail level backups on MS Exchange 2013 Cumulative Update 20 to Cumulative Update 23 or above using MAPI backup mode. To check the MS Exchange 2013 version and build number, use the Get-ExchangeServer cmdlet found in the Exchange Management Shell

Example: Get-ExchangeServer | Format-List Name, Edition,AdminDisplayVersion