Microsoft Exchange is large (often massive) database with each mailbox being a subset of that database.

Databases are prone to corruption.  Users experiencing issues with their mailbox such as getting bad search results would be likely candidates for this repair process.

You must be an Exchange Administrator or a member of the appropriate Role Group:  Organization Management

To start you should first check for corruption:

  • New-MailboxRepairRequest -Mailbox username -CorruptionType ProvisionedFolder,SearchFolder,AggregateCounts,Folderview -DetectOnly

If corruption is detected rerun the command without -DetectOnly