Same as PGP keys. Just post your public PGP key once, and anyone can send you encrypted information which only you can read across any medium they choose - email, PMs, instant messaging, chat rooms, Facebook messenger, Twitter comments, forum posts, you name it. Even better is that you can verify it came from the person you think it did by using their PGP key, with no need to have them message you over a different medium with a random string of characters.

Setting up a PGP key for the first time would only take marginally longer than OP's "disposable email plus forum message to confirm" system, but once you've done it once then it takes seconds to use it again in the future.