Rebuild search index of a mailbox in Exchange Online

Thanks for posted this information. We were experiencing the same problem that you describe. 

Messages were visible in the mailbox, however, when we would use search, in either the Outlook desktop client or the web Outlook / OWA client, the messages would not be found.

In our case there appeared to a small 3-month window in which messages were missing from the search results. SO we would see some older messages, as well as very recent messages. However, any that were within the three-month window would not be returned when searching.

This might have something to do with our migration process to Office 365. We used BitTitan to perform a pre-stage migration that moved all mail older than 90 days. Then after we switched to Office 365 live, we performed a full migration that picked up all mail within the most recent 90-day time frame. It seemed that these messages were the messages that did not get indexed by the search engine.

After using the New-MoveRequest -Identity user@domain.com command the search results are returning all messages.

One additional bit of information on the commands to use:

To start the move issue the following command:

New-MoveRequest -Identity user@domain.com

To check on the status of a move you can use either of these two commands:

Get-MoveRequestStatistics -Identity user@domain.com
Get-MoveRequest -Identity user@domain.com

Once the Get-MoveRequest status is "Completed", then you should run:

Remove-MoveRequest -Identity user@domain.com

The move process might take a few hours to even a day or two to complete. Mailboxes remain accessible and usable during this operation, so users should not experience any issues if the move is processing during working hours.

Richard