We have a AD domain with .local extension, that is different from our actual domain. So, at user object level in AD, Primary UPN: logonname@addomain.local
To implement Office365, we needed to have the actual domain. So when creating user objects, we set UPN as logonname@actualdomain.edu. So, the New primary UPN: logonname@actualdomain.edu.
After we changed the primary UPN, I am able to see 2 UPN dropdowns in the account management tab. The first one was @actualdomain.edu and the second one was @addomain.local(default).
We were thinking that, when users login, they can use either one of these @UPNs but as soon as we added the logonname@actualdomain.edu as the primary UPN, it broke the existing connection (@addomain.local). Applications with addomain.local\username broke. What are we doing wrong? Should we add alternate Upn(or UPNSuffixes) at domain level or at the OU level?