[Citadel Development] (no subject)

[IGnatius T Foobar]

Microsoft Lync (or as they call it now, "Skype for Business") is based on
SIP, not XMPP.  But it still doesn't interoperate with anything else. 
  
 So basically every major provider is killing off their support of standard
clients because they want to keep you inside their walled garden.