A user's UPN (used for signing in) and email address can be different. If you just need to add a new email address for a user, you can add an alias without changing the UPN.
Types of UPN changes
You can change a UPN by changing the prefix, suffix, or both:
Changing the prefix. For example, if a person's name changed, you might change their account name:
user1@contoso.com to user2@contoso.com
Changing the suffix. For example, If a person changed divisions, you might change their domain:
user1@contoso.com to user1@contososuites.com
Important
UPN changes can take several hours to propagate through your environment.
After you change a UPN, any saved links to the user's OneDrive (such as desktop shortcuts or browser favorites) will no longer work and will need to be updated.
Sync
The sync app (on both Windows and Mac) will automatically switch to sync with the new OneDrive location after a UPN change. While the UPN change is propagating through your environment, users may see an error in the OneDrive sync app that "One or more libraries couldn't be synced." If they select for more information, they'll see "You don't have permission to sync this library." Users who see this error should restart the sync app. The error goes away when the UPN change has been fully propagated and the sync app is updated to use the user's new OneDrive URL.
Note
Synced team sites are not impacted by the OneDrive URL change.
OneNote
After a UPN change, users will need to close and reopen their OneNote notebooks stored in OneDrive.
After a UPN change, accessing the OneDrive app in Microsoft Teams can result in an error: 404 File not found.
Until a fix is released, to resolve the error:
Create a 1:1 chat with another user.
In the message box, select Actions and apps> Attach file > Upload from this device.
Select a file you will send to the other user, then select Open.
Press Enter to send the file or select Send.
After you’ve sent the file, navigate to the OneDrive app in Teams.
Recent files lists
After a UPN change, users will need to browse to reopen active OneDrive files in their new location. Any links to the files (including browser favorites, desktop shortcuts, and "Recent" lists in Office apps and Windows) will no longer work.
Shared OneDrive files
If a user shared OneDrive files with others, the links will no longer work after a UPN change. The user needs to reshare the files.
Office Backstage View
After a UPN change, although Office will continue to work as expected, the user's original UPN will continue to be displayed in the Office Backstage View. To update the Office Backstage View to display the changed UPN, the user needs to sign out and then sign in using the Office client.
Search and Delve
After a UPN change, it might take a while for files at the new OneDrive URL to be indexed. During this time, search results in OneDrive and SharePoint will use the old URL. Users can copy the URL, paste it in the address bar, and then update the portion for the new UPN.
Delve will also link to old OneDrive URLs for a period of time after a UPN change. As activity occurs in the new location, the new links will start appearing.
SharePoint automated workflows and customizations
Any automated workflows that were created with Power Automate or SharePoint 2013 workflows and refer to a OneDrive URL won't work after a UPN change. Similarly, any SharePoint apps (including Power Apps) that reference a OneDrive URL will need to be updated after a UPN change.
Recommendations
If you're changing many UPNs within your organization, make the UPN changes in batches to manage the load on the system.
If possible, apply changes before a weekend or during non-peak hours to allow time for the change to propagate and not interfere with your users' work.