Error: MigrationRecipientNotFoundException: A recipient was not found for “mailboxName”

If you received the error “Error: MigrationRecipientNotFoundException: A recipient was not found for “mailboxName”” when migrating a mailbox to Exchange Online (Office 365) then check for the below AD attributes.

The error from the Exchange Admin Portal on Office 365:

Open the on premises Exchange Management Console and search for the user. You should see the mailbox shows it’s a Linked Mailbox instead of a Remote Mailbox as expected:

To rectify this, open AD Attribute Editor and browse to the msExchRecipientTypeDetails attribute. You should see the below:

Change the Value of 2 to 1 for msExchRecipientTypeDetails as you need the mailbox to show as a user mailbox on premises before trying to migrate it to Exchange Online.

Wait for replication, remove the move request in Exchange Online via Shell and then migrate the mailbox to Exchange Online