Something came up last time Sourceforge was discussed here, namely "why are projects still using it?"... I'm the project lead for LXQt ( http://lxqt.org ). We inherited some infrastructure legacy from LXDE, which was hosted on sourceforge. Today, we have moved most of the legacy to Github but we're still using Sourceforge's mailing list system. We're moving to a self-hosted mailman3 instance but it's been excruciatin…
Why mailing lists are still quite massively popular in 2015?..
Because (your email client) is always going to be much, much faster and easier to navigate than "some dudes cute forum setup".
Replying to and managing conversations is much easier when you can do it with one or two keystrokes rather than mousey-mousing ten clicks all over the place (and oh their ad tracking js is stalling out again...)
I maintain that all web forums should have a mailing list interface so that you can use the forum without using the web at all ... but I suppose that breaks their revenue model ...