Start a Q&A forum
Get yourself a Q&A forum instead of using mailing lists. You can use Stack Exchange (beta, will cost money soon) or Shapado (free & open source).
StackOverflow fills in this role beautifully
AdminJohn Simons (Admin, Castle Project) commented
I'm for that as long we close the users mailing list.
Why not stick to StackOverflow? I like it, and many Castle committers and long-time users answer questions there. I don't think we need a dedicated site for that.