OOC - Communications

Hello again, friends!
Something I have run into recently, and I'm sure the rest of you have, as well: when a player does not have a valid email listed on their account.
I recently had an interesting character submission come across my game, and the character was pretty well thought out, but maybe a little overpowered. In response, I sent the player and email going over my concerns and suggestions, so that we can address them before I accept their character into my game.
However, the email returned undeliverable.
One thing that I feel will highly assist gamemasters with situations like this would be some sort of messaging system on OGW itself. Relying on email can be hard if a user fails to update theirs on their account.
This would provide us with a way of contacting others without having to use OOC posts, especially if you need to contact one player in particular, but don't want to out them to the others in-game.
I would like to see if anyone else shares my thoughts on this matter, or if you do not, feel free to explain why.