Without seeing the code you're working with (which you can post here, to make an answer more helpful: when you cut 'n' paste it in, put a <code> in front of it and a </code> at the end) - without seeing the code it's hard to be sure what's not working, but I think to start with you need to get your users to put in their emails - otherwise, not only will the people replying not know the email, *nobody* will.

update: substituted </code> for <code> and vice versa so that the above ceased to be idiotic... with thanks to screamer

§ George Sherston