You can control notifications for the OSX Group Chat directly inside the app.
Open Messages from the bottom menu.
Open the OSX Group Chat.
Tap OSX Group Chat at the top-left of the screen.
Use the Notifications switch to turn group chat notifications on or off.
Turn notifications off if you don’t want alerts from the group chat. Turn them on anytime if you want to receive group chat notifications again.
Note: This only changes notifications for the OSX Group Chat.


