I need to change the User ID that is being used to login to Office 365. We have an on site Exchange 2010 server and have migrated to Office 365. Our current domain and email address is firstname.lastname@example.org and Microsoft created us a domain called 123.com. My users really have two email addresses, email@example.com and firstname.lastname@example.org. This is fine and we are using AD synchronization which is working fine.
However, it makes my users log into their accounts with the email@example.com account when accessing email or 365 in the cloud. But at work in our domain, they are accustomed to using firstname.lastname@example.org. Is their a way I can make it allow them to login with the other account id instead of the one Microsoft created?