When you move a mailbox to Exchange Server 2013 or Exchange Server 2016 within the same forest from an earlier version of Exchange Server, the mailbox quota is not validated during the migration process.
Mailbox moves are completed successfully even when the mailbox size exceeds the quota limits of the target database. In this situation, users can't send or receive email messages after they're migrated to Exchange 2013 or Exchange 2016.
This issue occurs because quota validation is skipped within the same organization when you use the New-MoveRequest cmdlet.
To fix this issue, install one of the following, as appropriate for your situation:
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.
After you install this update, the New-MoveRequest cmdlet performs a quota validation check and blocks mailbox migration if the size exceeds the quota limits that are specified on the target mailbox database.
When a mailbox is moved from an earlier version of Exchange to Exchange 2013, the reported mailbox size may increase 30–40 percent, as described in the Mailbox section of the release notes for Exchange 2013.
Learn about the terminology that Microsoft uses to describe software updates.