Please use the following steps on The message exceeds the maximum supported size. Cannot save changes made to an item to store (MS Exchange mail level restore).
When performing an MS Exchange mail level backup (both Exchange server and Office 365 mail level backup set), the following info message is displayed in the backup client log:
This video provides instructions on how to utilize the RunSingleUserRebuild.do (with CheckCRC option enabled) to perform a Cyclic Redundancy Check for legacy backup sets created in version 6 for backup clients installed on operating systems