[OT] Mailing list software for windows

[TealC]

Hi

A friend of mine and me, we host a MS Exchange Server for private mailing. (approx. 25 users) Until last weekend we had the GFI Mail Essentials installed. Now we switched for the ASSP spamfilter (which is brilliant btw, can do almost any spam filtering method --> assp.sf.net) but now we are searching for a replacement for the Mailing List function, which was pretty useful in GFI Mail Essentials.

I'm looking for a tool, which has its own smtp server, and which allows you to subscribe / unsubscribe and post by mail. So pretty much a basic mailing list software.
requirements are:
- has to run under windows 2003 server
- port for smtp communication must be configurable (since there's already ASSP listening on port 25)

and that's pretty much it.

Does anyone know such a tool?

Thanks in advance
TealC