Connecting to Lync Online [or Skype for Business] using the Messages App

See this link.

Basically, you have to edit the plist for Lync, and enter a registry key equivalent.

The explanation is below:

Basically, the equivalent to the registry keys for windows needs to be entered in the Lync config plist file on the mac, a file named MicrosoftLyncRegistrationDB.xxx.plist that you can find in ~/Library/Preferences/ByHost.

In it, you will need to create an entry for each segment of the reg key path for the DisableServerCheck flag (all lower case). It should look like this:

hkey_current_user\

hkey_current_user\software\

hkey_current_user\software\policies\

hkey_current_user\software\policies\microsoft\

hkey_current_user\software\policies\microsoft\communicator\

hkey_current_user\software\policies\microsoft\communicator\disableservercheck

The value for each of the path segments is "<>" and type string. For the disableservercheck flag, the type is "Number" and the value is 1.

You can use a plist editor (there's a few free ones for the mac, or you can also use Xcode) to edit the plist file. The screenshot below shows you how it should look like.

You may want to set your status to Offline. Or remove Skype app from the running task list (double-tap on Home, switch into Skype area and swipe to the top to get rid of it).

If that won't work and it changes back to Online, this potentially could happen when you're logged into your account multiple times from different devices, so the statuses could be not in sync.

For workaround there are some cloud-based chat commands which allows you to see where you're logged in and you can logout from the remote sessions.

1. Create an empty conversation.

2. Type command in the message textbox:

   /showplaces
   

   Lists other endpoints that can receive push notifications for calls and IMs for this Skype account.

3. If you want to logout from remote online endpoints, then execute:

   /remotelogout
   

   Sign out all other instances except the current one. This will also stop push notifications on all other instances.

Other workaround could include changing your Skype password to make remote Skype clients sign out.