Mailbox migration failed leaving user on-prem and in the cloud

Question

Hi all,

I had a very odd migration experience with a client.

1. The users mailbox was autosuspended and ready to cutover,
2. We ran the command to cut them over to Exchange Online.
3. The migration request disappeared from the move request output.
4. The user's mailbox remained on-prem but the cloud mailbox became active.
5. Outlook desktop continued to connect to the on-prem mailbox, but the user was able to login to cloud OWA and use the cloud mailbox.

The issue was resolved by removing the license and permanently deleting the cloud mailbox, but what could cause this and where would I even look? The move-request completely disappeared from exchange online for that user so can't even say i would look there.

This one is a real head scratcher. Any ideas?

Environment version: Exchange 2019 CU15.

Answer 1

Hi Raymond Brooks,

Thank you for posting your question in the Microsoft Q&A forum.

Do you check from Exchange admin center in Exchange Online directly to confirm if any migration batch exists in Exchange Online? In general, the cutover migration batch should be deleted manually.

Here are some suggestions for you:

1. If this issue only occurs with specific one user, please make sure that the recipient is not hidden from the address list in on-premises Exchange server.
2. You can re-create a migration bath and only to migrate this problematic mailbox to see if the mailbox could be moved successfully this time.
3. For outlook client side, please try to create a new Outlook profile or test with other client computer to avoid any Outlook cache after completing the migration.

---

If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".

Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.