Email VS Login ID

[DJToested]

Our business uses login IDs for authentication to Teams.  Our Global Address List shows email address, obviously.  BUT, when someone wants to Teams a member of our business by browsing the GLobal Address List, it fails because Teams does not recognize email addresses, only login IDs.  Is there a way on the back end to sync email address via Global Address List to Login ID so that Teams will work, and the Login ID be hidden from the public?  Thanks in advance!

[#2]

Is display name populated?

[#3]

@adam deltinger 

Yes it is.  We have to follow a strict template for our agency, so the Display Name is populated by "last, first@xyz.com"