Google Feedburner still works. You can also use it for creating mailing lists.
1. Create a blogger account for your site.
2. Create an IFTTT account.
3. Add your forum's RSS link to a Blogger recipe.
https://ifttt.com/blogger
4. In blogger's dashboard go to Layout/Add A Gadget/Follow by Email.
5. Change the title of that widget to: "Mailing List"
In your footer just link to your site's blog that has the mailing list widget.
You can see your subscribers in Google Feedburner by clicking Feed Stats and "Feed Subscribers"
