This is already available. You'll find a Subscribe link on the page with the list of topics in a forum, just as there's a Subscribe link in each topic itself for each post received on that topic. Be aware that you only ever get one email at a time for a given topic; you have to come back to the board if you're to receive more, which is a bloody stupid limitation and one of the chief motivations behind the creation of the reflector.

The audiogames-reflector list will send you every single post on every single topic in every single room, unconditionally. It delivers HTML email that's threaded by subject, so you can use your favourite email client to dice up the forum content without having to mess about with visiting each forum or handling the substandard email notifications that the forum software generates. It's high-traffic, so you're advised to filter the email into a dedicated folder. But if you need this level of email fandom, it's on offer. I have relatively few subscribers but those that have all seem to be sticking around, so I think it's fair to say they like it.