Ahh yes...  copyself, junk, main are all there.  Good to know, thanks.

The follow error displays upon completion of "recover deleted space" operation:

Error compressing folder!

A serious error has occurred while Pegasus Mail was compressing this folder, and data may have been lost. You should exit from Pegasus Mail as quickly as possible and use an undelete utility to recover the files copyself.PMI and/or copyself.PMM.

I close Pegasus and go look for those files, and copyself.PMI has indeed been deleted.  I can reopen Pegasus, perform a reindex on the folder and the file will recreate, but still, if I try to recover deleted space again, the same error occurs and the same file is deleted.

Any suggestions?

what is the current file size of the copyself.pmm? If near or over the 2gb limit of windows filestore -- could be a problem.

Thats actually of the interesting things.  The Copies to self counts that there are some 9000 message in it, but the copyself.pmm file is ~10mb.

Either way it turns out, I managed to fix things:

I moved all the message from the folder to a collection of others, deleted the copyself.pmm and .pmi, created a new folder in Pegasus, and then renamed it and it's .pmm and .pmi files copyself.pmm/pmi.

New copyself files are available in the Defaults folder within the Programs folder.