Reply to Post Notification creates a Reply/Post on the Forum

I am losing membership because groups are going to www.clubexpress.com where they support web-based and integrated email discussions.  They've been able to successfully convert Yahoo! and Google mailing lists to their forum.

Question:  What is required to allow recipients of forum notifications in email to reply and then have their email show up as a real forum post?

I know this is dinosaur stuff, but it's what people are used to...