I'm looking for a way to insert checkbox fields into an email, so when you reply the email you can send the checked fields!
Using PHP I have create an HtML email but when I reply, the checkbox fields lose values.
This can't be done the way you try to do it. E-mail clients are very limited in functionality and do not work the same way normal webservers do. What you should do is have the form on your server, then link to it to have the users come to your site to fill it out. The tricky part is getting the users intrested enough to actually bother to fill out your form.