My suggestions should be useful for cases when you would messaging a group of players that is located around a POI. You would click on first player, select popup item "Message". When a new message window will open - you shift it, select another player, click "Message", ... until all players will be in recipients.
After that you click on the POI the "Paste coords" - and POI coords will be copied to message body. And you add a message like "Join to alliance or get away from the POI. You have 24 hours only !" :))) or "Go together to get another useful POI" ...
Now if mentioned group of players are in another alliance you don't have easy methods to messaging.
Another problem. My alliance members often send message to ALL players in alliance without filtering the recipients, even if the problem is local and have relation to 2-3 players. In my alliance the number of players is ~48 so players often don't like to delete extra recipients.