M365 Tenant to Tenant Migration

Brass Contributor

Hi Community,


One of our customer currently migrating some OneDrive DATA from their old tenant to a new one. Customer wants to keep same domain names.


So they must first remove them from the old tenant to create them in the new one. But they're afraid to loose the (OneDrive) DATA associated with the accounts when they will be moved to the initial ".ONMICROSOFT.COM" domain (which will happen after domain name removal).




1. What exactly happens with the accounts of OneDrive DATA once the old domain (wherein it was originally hosted) is removed ?

2. What is the best practice in this context to retrieve any associated DATA during/after migration?


They want to check the priority steps knowing that they want to keep its domain name in the new tenant, which mean they'll have to detach the domain from tenant source to create it in target tenant


3. Should they first create a temporary domain where users will be migrated to, remove the domain name from tenant source to free it and create it in target tenant, then create the users ? or can they simply remove the domain name which will cause the existing users belonging to this domain to be automatically moved the initial .ONMICROSOFT.COM domain (with all the dependencies and OneDrive Data) ?


Any pointers would be of great help!


Many thanks in advance!

2 Replies

1. Nothing happens to the data. The UserPrincipalName will be changed from email address removed for privacy reasons to email address removed for privacy reasons. The user can login and access the data, by using the .onmicrosoft.com domain name. So keep in mind the user impact on the end-user and tell them how to access the data if needed.

When migrating OneDrive data, try using Mover.io (free Microsoft tool).
1. Create all users in the new tenant (you don't need to attach the domain at this point, the .onmicrosoft.com domain name will work just fine).
2. Set-up mover & sync OneDrive from accounts in the old tenant to accounts in the new tenant.
4. When synchronisation is done, delete the domain name from the old tenant and attach it to the new one. This can take a while (around 30 minutes).
5. Users can logon on the new tenant and the OneDrive data will be visible. The old data isn't deleted, so if something is missing, they still can logon to the old tenant with the .onmicrosoft.com domain name.

Aks the users to limit the use of OneDrive during migration if possible (with small seat-size).
if you want to move your domain, there will be a short downtime while detaching the domain from the source tenant and reattaching to the target tenant.
This can be addressed with a temporary mailrouting: