Just out of curiosity and because I like archiving everything I wanted to convert my Pegasus Mail folders to Unix mailboxes. The format of the .pmm files is simple, you can guess it opening one of the files with vi, and this script converts those files.
The pegasusmail2unixmailbox.py package is released to the public domain. You can do whatever you want with it, and you are responsible for yourself. Basically, imagine this simply appeared on your hard disk and don't make questions.