Couple of similar but useful alternatives:
- Starting a thread dedicated to this very purpose. Announce that you are preparing to join the server and join. Those who subscribe to this thread will get e-mail notificatrions.
- Starting a sub-forum for this very purpose. Game requests only and is invite only so only those who wish to can tell/be notified of players who are actively seeking opponents.
- Starting a group that contains only people who want to be notified. Players interested in announcing will PM the entire group (Search For Player -> By Group -> Select All).
Each of these options will achieve the same result without the automation and potential abuse of having a script e-mail everyone anytime a lone player enters. I imagine those willing to be on the list wouldn't mind making a post shortly before joining a server. (Or even while on if nobody is there).
Do any of these sound useful?