While I was working on a Office 365 migration project with a colleague at a customer with a Lync on-premises environment, we were facing problems with logging in to Lync Online with federated accounts.
If you are moving to Office 365 you probably want to phase out your current on-premises Lync environment. If you do so, you have to update some user properties in your Active Directory before you can login to your Lync Online environment:
|Active Directory attribute||Attribute name||Correct value Lync Online||Correct value Lync on–premises|
Make sure you start a sync on DirSync after updating these properties. The new way to do this is with the latest version (6862.0000) is to start PowerShell and run the following commands:
Import-Module DirSync Start-OnlineCoexistenceSync