As for the usergroup permissions...I don't think there are any. Someone asked earlier of Mod's could use this too but global mods & mods don't need to do this unless they're the group owner. Otherwise this is simply for the group owner.
But I did notice when you're on the Mass PM Social Group Members page none of the Navbar menu drop down links work.
Also I'm wondering if the fact PM's are being sent for members awaiting approval & invited members who haven't decided to join yet has been fixed yet.
Also I'm wondering about a "save a copy" option.
Thank you for this mod.