How can I migrate on-premise exchange 2019 users to M365 if they are already added as guest users in the onmicrosoft.com tenant and have Teams conversation history that needs to be preserved?

Question

I have an exchange 2019 on-premise server and I want to migrate to M365.

There are several tenants on the server and I can't perform a cutover migration since it will take all mailboxes from all domains on the server.

I am exploring the IMAP migration and wanted to create the users in M365.

However, I encountered this issue: On-premise users are already added as guest users on the onmicrosoft tenant. As guest users they are already using Teams and have a rich conversation history that needs to be preserved.

How can I migrate the emails of the users and keep Teams history and have in the end the on-premise domain email address as main username and not the guest added one?

Thank you.

Answer 1

Hi @Corneliu Maresciuc

To migrate the on-premises users to Exchange Online, you may first need to create the corresponding Azure AD accounts (which is supposed to be another account than the guest account) and assign licenses.

However, to my knowledge unfortunately it is not supported to convert a guest user to a member (to be used as the corresponding account for the user to be migrated) while keeping Teams conversation history.

Please refer to this link: Guest access in Microsoft Teams

And there is no supported method or tool to migrate the Teams conversation history by Microsoft.

If possible I would suggest looking for some third-party tools to see if you can migrate the Teams data from the guest account to the new account.

---

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.

Answer 2

In summary, to migrate from an on-premises Exchange 2019 server to Microsoft 365 while preserving Teams history and retaining the on-premises domain email addresses as the primary ones:

1. Perform an IMAP migration for email data to Microsoft 365.
2. Investigate the latest guidance on preserving Teams history during migration from Microsoft.
3. Convert guest user accounts to full Teams members after email migration.
4. Change the primary email addresses in Microsoft 365 to the on-premises domain addresses.
5. Update mail flow settings to route emails to Microsoft 365.
6. Thoroughly test and validate the setup.
7. Communicate the migration plan to users.

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