Filing Mail in Arbitrary Folders

Hi,

I have several years' worth of e-mail folders spread throughout my 
system (Sun Ultra running Solaris 9). Currently I use mozilla to pop 
mail over from my ISP. I read the mail and filter spam in mozilla, and 
then move the keeper messages to my inbox, /var/mail/rod. Then I use
dtmail to respond (because it creates a record of the response in my 
home directory, but I can live with the record file buried in the 
mozilla hierachy under my home). I also use dtmail to file messages in 
the appropriate folder. While I have several folders pre-defined in 
dtamil, I use many others that aren't pre-defined; dtmail has a good 
interface for dynamically choosing those folders.

This works well except that dtmail does not properly handle and display 
multipart messages. All I see is the header fields. I am told to use 
something other than dtmail, and was pointed to t-bird. Hence my 
previous question about mozilla wrt firebox and t-bird.

My concern is that filing messages directly from mozilla or t-bird will 
require me to have all my folders in the mozilla hierarchy. And I am 
concerned that I will have to statically define all those folders to 
mozilla.

Is there a simple way to move a message from my mozilla inbox to an 
arbitrary folder anywhere under my home directory? Can you point me to a 
cookbook description of how to do that?

Thanks!

Rod