You can, although not from within the program. Right mouse on the folder in the folderslisting and go Folder information.You will find the file name in there.

Now close down Pegasus Mail and go to the Home mailbox directory. Copy (do not move) both the <name>.PMM and <name>.PMI file to any other place you want. Restart Pegasus Mail and delete the folder.
 

To restore, just copy both files back and restart Pegasus Mail. 

FYI:

* Problems after restoring mailbox files from CD-ROM *

Q: I backed up my Pegasus Mail mailbox directory to CD-R (or CD-RW or DVD or whatever) and restored it after a hard drive replacement (or Windows OS reinstall).  Now everything is behaving very strange.  I cannot delete new mail messages and my mail folders say they are corrupted.  Also, I can't make changes nor add addresses to any of my address books.  Additionally, changes to my WinPMail configuration settings don't get saved anymore. What's going on? 

A: When you restore files from CD-ROM-based technology, the OS usually sets read-only flag on each of the files.  Thus, WinPMail cannot make changes to the files anymore.  To fix this, select all the files in your mailbox directory and press Alt-Enter (or right- click on the files and choose Properties from the popup context menu).  Uncheck the Read-Only checkbox and click OK. 

I am an architect working with autocad and graphic files and I receive a tremendous amount of mail with very large attachments. My folders get very big very quickly, and once a project is complete I would very much like delete the folder and save it onto a disc, in such a way that I can access it again, or copy it back to my harddrive should I need to.

I have always like the simplicity of Pegasus which allows me to backup the entire programme onto discs and then onto a new computer without being forced to reinstall from scratch. I just wish there was a way I could save each folder separately.

The other thing I'd like is to be able to separate which attachments go to which person on my distribution list. I know this is probably too complicated, but because I work with specialist programmes,often some of those on the list cannot read the files, and I create pdf files for them. It would be nice to be able to tick off which attachments go to which people.