In effort to migrate our Exchange 2010 users to O365, we have discovered we have a lot of users with duplicated UPNs.
For ex, in the attached, the user login using adlopez but her User Logon Name in AD is "alopez". There is also another users with that User Logon Name.
1. Can I just rename and enter adlopez in the User Logon Name field without causing any issue?
2. Is User Logon Name is the same as UPN?
The best practice in your case is to use a specific tool for your scenario. IdFix tool will help you to proceed and change duplicate attributes as UPN.
You can find this tool here : https://www.microsoft.com/en-us/download/details.aspx?id=36832.
Let me know !