JG zimmele - erm you are wrong. Maling list handling works just fine - I tried it just last week. And, if you don't have filtering/spam services on your *server* then you (probably) shouldn't be using IMAP. The purpose of IMAP, at least as far as MPro is concerned, is to display messages resident on a remote mail server - eg. a work mail server, or a university mail server. Thus to have filtering in this context, in the *client* would seem to be a nonsense. I have seen IMAP used as a fetch protocol on some platfroms, with the results stored locally. In this context, filtering would make more sense. However, MPro's philosophy is for mail to remain on the server.
To use the Mailing List facility, you need a folder on your server to contain the mail list postings, exactly as in offline Mpro, then mark said folder as a "mailing list".
I suspect in your case, it sounds like you need a more flexible/better configured server. Even Mpro server would allow you to configure filtering etc. server side to avoid your problems. I appreciate you may not have server access, but really that's not MPro's fault.
Actually thinking about it, what you need is the ability to apply some kind of "effect to messages already received" which is what scoring is all about, but currently scoring is non-destructive (ie. won't move stuff around).
Oh, incidentally, I think scoring works with IMAP too, since it is part of Mpro client, not the MsgServe server.