Office 365 user mailbox shows 'mailbox hasn't been migrated to Exchange Online' error

Problem Description : 

The error "This user's on-premises mailbox hasn't been migrated to Exchange Online. The Exchange Online mailbox will be available after migration is completed." can occur when a former employee's account is disabled and moved out of the User OU but then is rehired and the Office 365 account is re-synced and created (without creating a new user account).

 Resolution : 

User shows the message "This user's on-premises mailbox hasn't been migrated to Exchange Online. The Exchange Online mailbox will be available after migration is completed." under Exchange Online.

In order to fix follow these steps..

1. Move user account back out to Disabled Users OU and allow ADConnect to sync.

2. Perform a hard delete on the account in Office 365 Powershell (once it moves to disabled users in the cloud).

Remove-MsolUser -UserPrincipalName user@gordonstate.edu -RemoveFromRecycleBin

3. In Active Directory, clear out the users msExchMailboxGUID attribute.

4. Move the user back to the Users OU to allow ADConnect to sync the user again.

5. Once the ADConnect sync is complete the user should have an Exchange Online mailbox created now.

 Revision Date : 6/25/2019