Well, the simplest option is to have each of these "archive" mailboxes in their own directories on your hard drive and then use the Folders -> Add Mailbox To List... menu option to mount each of the additional archive mailboxes.  You can then move or copy emails between folders in the different mailboxes.  However, you cannot simply move a folder between mailboxes (hopefully a future version will allow that).

How to put mails from 5 different computers together?

 I used Pegasus since forever. And, whenever I moved, I simply made a backup of my emails and started afresh on a new machine. In years, I got backups from say, "1998-01", and "2004 only" and "2001-2005, without 2004".

 
I need single copies of all mail stored in all these backups! 

There are a lot of folders, a lot of them of the same name, but different sizes and contents, lots of email in "new mail" (*.cnm).

I wish I could just upload them all into Pegasus and then have a utility that would purge duplicates (triplicates...). Lately, this problem even made me use Webmail as I just dodn't want to have another "One year of Pegasus archive" CD...

Please think of a Pegasus solution.

Simple "put backup into mail directory" would of course fail, I tried some renaming but failed (even without the burden of manual renaming), then used dragon-it.co.uk Folder converter to try to put it all into Netscape (and load to Thunderbird, purge duplicates and then get it back to Pegasus somehow), BUT, the Mail system converter only converts folders, what do I do with all the pm$ and cnm files?

 
Here are some file lists from backups:
http://mitja.org/PMAIL/

Many, many thanks.

(to community and to David for going on) 

Another idea:

copying all CNM files (from various backups) to the same /MAIL directory.

That would solve the new-mail problem, but folders would still need to be converted and duplicates purged via dragon-it-tool and duplicate finder in Thnuderbird. Dragon-it mail converter is sweet, as it adds new messages to existing folders, doesn't overwrite them.

 Or is there a duplicate finder utility for Pegasus?

 
It is hard to believe no one had a similar problem in the past.