Today I noticed that Outlook was not showing the presence of my contacts anymore. It appeared they were all offline. However, when I checked their status in Skype for Business, they weren’t offline.
Outlook using a registry key to identity which IM Provider is integrated. That registry key is HKEY_CURRENT_USER\Software\IM Providers. You will find a value under IM Providers called DefaultIMApp. When I checked the value it had changed to Teams. Since my organization hasn’t migrated to Teams yet for their VOIP I didn’t need that value. I need the value voor Skype for Business which is Lync. So, after changing the value back and restarting outlook the “issue” was resolved.