i believe that that would be the best way to go aobut it. Connect to the pop3 bobx and check for new mails. it is much better than piping all the email throught a script.
is there any way that it can be done like

$subject=Email posting
$body=i like this email posting stuff.

but that might be to complicated. are you going to do it so that the subject line tells where the post should go? or the email adress says where to go.

i don't think that the user will get every email posted in a particular forum. i think that the user should be able to post from his/her email. and when someone replies to his/her email they will get the replies. and instaed of having to go to the forum the user should be able to reply to the email instead of having to go the forums to post.

i don't think that it should be an email discussion list, but a way for users to post/reply via email.