Microsoft Exchange: Slow initial backups of large mailboxes
The initial backup of a Microsoft Exchange mailbox with a large number of folders is excessively slow and takes longer than expected to complete.
Environment
- Datto SaaS Protection 2.0 for Microsoft 365
Cause
This performance issue can manifest when attempting to back up mailboxes where the total number of folders and sub-folders exceeds 1,000.
During the initial backup, the Microsoft Exchange API must paginate and sync each folder. The process of parsing large numbers of folder layers takes longer than top-level folder.
Resolution
This limitation originates from the Microsoft Exchange service. Allow the initial backup to complete. If it does not, or the time to completion becomes unacceptable, contact Microsoft support for assistance.
