There's no way of knowing whether they have seen the message. I think I've only sent 2 messages but one of them was to correct my previous mistake in not including an email to reset the account too. I wish they would let you know if they have received the message and are looking into things.
If they replied then they seen it but if not then they don't. You slipped that chance when they seen your mail but unfortunately you forgot to attach your email so all you got to do is to wait.
Maybe thats something to new forum can have is a "seen" button.
I'm not sure if it really is included but that's a nice idea like in messenger.