Cerulean

Ugh. I'm gonna share in DaWei's distress on this one. What is it with the amount of people who can't gracefully take correction?

XHTML/HTML, of course. It's not an XHTML only thing. As said before, it's subject to disabling on the client side. The mailto protocol is just a nifty way for a webpage to try and tell a web-browser to open up a compose email window with some information filled in, nothing more. Any method that opens a new webpage that begins with "mailto:" falls under this category, so using an anchor, a form submit, a meta page refresh, a JavaScript window re-direct, whatever, will do the same thing.

If you want a slightly more full-proof method create a server-side script that uses tools on the server to send an e-mail using whatever programming language you choose (PHP has the built-in mail function, for example). You can then create a HTML form and pass the text from a textbox in the form to the server-side script that will send the e-mail. Voila.