I don't think you can prevent individual members from sending you messages except by blocking them one-by-one.
But you might try posting a message on your profile page: "I DO NOT PLAY TEAM MATCHES OR VOTE GAMES". I think this might discourage many of the group invitations (hopefully they look at profiles before send invitations).
I have been recieving dozens of messages every day which is really annoying! The majority of these messages are invitations for team matches . I can't say I am not intrested but it's irritating to have 60 to 70 messages every day!
Please is there sth to do to stop receiving such messages?????
I need help!
Yours,`
~John~