Hey David. I use Messenger for mail and have since it came out. The UNIX version has a few "features". I use a structure like this: Inbox debian-devel ... debian-user linux-arm linux-parport etc.
As the folders get larger it no longer shows new mail. However clicing on the folders causes it to re-read the database and show the new messsges. Make sure in the filter rules you tell it to go to the right filter. NS uses its own folder format. Do not think exim or what not can read it. Need detailed help contact me for one-on-one. -- ===== Linux, because I'd like to *get there* today