Consider you posted your protonmail addy on a public www channel. You would receive quite some spam.
I posted it months ago, and haven't received any spam.
6. TMM address expires after ten minutes, as usual. All traceable data should be lost.
But you can't verify that, so you have to trust them on it. "Trusting" isn't very "Bitcoiny".
If you want to send another user a message without exposing any private info like an email address and without any risk of it being intercepted, then just have them provide you a PGP public key, encrypt the message, and send it through a private message.
I'd have to manage additional keys. Not easy for a guy with memory problems
PGP keys aren't ment to be remembered, just store them safely. It's annoying to setup though.
How cool would it be if the (new) forum would implement client side PM encryption by default?