Basicly its not that easy ^^. A user in the guest group dont has to be new.Do you want someone who writes the script for you or need help writing it?
Shouldn't be too hard, probably the only thing to do is to check if a connecting user is in no server group and the message all configured user id's.
Ok, I assumed, the notified admin would assign the new user a group like "known-user" or so, which would solve this problem.Basicly its not that easy ^^. A user in the guest group dont has to be new.