Well I've had to get an e-mail removed from an account before, I was the owner and never left the account out of my hands or whatever but I just forgot what email I had set it to. There's a jagex support email, I'm unsure of what it is but from browsing the RS forums or FAQ you'll find it no problem.
Basically the way to sort it out is to email that address with a paragraph explaining how you don't remember the password or something for the email you have registered it with, and you would like to change it. In the email, you need to write as much information you can about the account, such as if you were trying to recover an account, that sort of information.
When I had to do this, I used recovery questions, First/earliest passwords, as many billing references as I had and I got a response after 3 weeks. It shouldn't take that long, But I had sent it in at a busy time.
