I recently ran into an issue with a customer that took me a while to get a solution for. While doing a hybrid migration from Exchange 2003 to Exchange Online, I had one user whose email alias showed up as firstname.lastname@example.org instead of the expected alias of email@example.com in the Exchange Online tenant.
The user’s alias was set correctly in the on-premises Active Directory, and no changes we made to AD would correct the users alias in Exchange Online. I believe that this was caused because this user setup his first administrator account in his tenant with the same alias as his on-premises email account. The solution for this issue is as follows
- Download Windows Azure Active Directory Module for PowerShell
- Connect to remote PowerShell for your tenant
- Run Set-MsolUserPrincipalName –UserPrincipalName firstname.lastname@example.org –NewUserPrincipalName email@example.com
…and you’re good to go.