can't be done realistically without having a form based on a website... if your doing it through email you would be required to send the person the form which they would then return to you thus doubling the communication.

My email server would also block this as I do not allow HTML based emails for viral reasons, some email clients would display a pure text email and the HTML form would be an attachment.

Modifying the code in your own form before emailing it back could be a fun way to exploit your system as well.

this is without considering how spam filters handle this form

I would personally consider running a small server from your own net connection for this purpose