Today it seems as if our mailing list server has died. Thankfully, we where in the process of moving them over to the KDE infrastructure in conformance to the KDE manifesto.
You can find the new addresses on the mailing list site.
There are two active mailing lists for KDevelop. On one hand, there is the User list, which is aimed at support and general discussion around KDevelop. Furthermore, there is the Development list. Here all important discussion around future development of KDevelop takes place. If you want to start contributing, you should at least follow the latter.