UserAlreadyBeingMigratedException: The user 'Name' already has a pending request.

A hybrid move to Exchange Online fails because an active or orphaned move request already exists for the user.

Why it happens

A move request already exists for the user in Exchange Online (the error adds Mailbox 'Name' is already being moved to 'Cloud Database Name') or in on-premises Exchange (the error reads MigrationPermanentException: The onboarding move could not be created because user 'Name' is already being moved). The old request can be active or orphaned, meaning left behind after a finished or failed move.

How to fix it

1. 1

   Step 1

   Run Get-MoveRequest for the user in the on-premises Exchange Management Shell and in Exchange Online PowerShell. The old request is usually Completed or Failed.

2. 2

   Step 2

   If the request is not part of a migration batch, remove it with Remove-MoveRequest. If it is, remove the migration user from that batch or remove the batch, which removes the move request.

3. 3

   Step 3

   If neither organisation shows a move request, open Active Directory Users and Computers on a domain controller, turn on View > Advanced Features, open the user's Attribute Editor tab and look for values in the msExchMailboxMove* attributes, such as msExchMailboxMoveRemoteHostName. Note each value, then clear it. Take care: wrong attribute edits can cause serious problems.

4. 4

   Step 4

   Create the move again, for example in a new migration batch.

Get-MoveRequest -Identity 'user@contoso.com'
Remove-MoveRequest -Identity 'user@contoso.com'

Source

Full guide: How to migrate from Exchange Server to Exchange Online →