Have you ever tried Becky! for windows machines? http://www.rimarts.co.jp/becky.htm
It's commercial but geebus, it's lightweight and powerful. Especially good for developers and others still using mailing lists.
have a look at http://www.rimarts.co.jp/becky.htm
small, fast, stable, super plugins and customization, (costs a few $$$ though - trial is infinite).
been using it for years, no standalone compares.