Please note that it is now possible to configure an alternate login ID (in some circumstances) for Skype for Business/Lync. This will most likely be of interest in cases where end users have email or SIP addresses that differ from their UPN and/or a UPN that is non-routable (jdoe@contoso.local).
You can read full requirements and other important technical details in the Windows IT Center.
Configuring Alternate Login ID
