Well, that works like a champ. I'm now able to cut large numbers of messages, and the right-click method does NOT kill the folder. Thank you!

UPDATE: Spoke too soon. I can delete fairly large numbers of messages. Too many, and poof, the folder is deleted. It's a workaround, but that will have to do.

Just upgraded to from around 4.5 to 4.6.3 under Win 7 64-bit.  Ran PMail and noticed my "Old Mail" folder (FOL06D6B.PMM) - but not the index - had somehow been deleted (477 Megs, some 15 years' worth of emails). Restored the PMM file (but not its PMI) from a backup I did just before the upgrade.  (In hindsight, Yes, that was stupid.) To do so I first had to rename a newly-created FOL06D6B file. 

Ran PMail, retrieved a few messages, checked some in Old Mail.  Headers didn't match the message, so I reindexed. All was well, I thought. Closed, reopened, deleted a few Old Mail messages, and closed again.

That's when I got "A serious error" message suggesting an "undelete utility" to recover "FOL06D6B.PMI

and/or FOL06D6B.PMM".  The PMI file is still there, but the PMM file is not.

Should I... 

1) ask for recommendations for a good undelete utility?  Or would restoring the file just lead to more problems? 

2) start over and restore the older C:\Pmail from backup? I'd lose the new messages, which would be inconvenient, but not as much as losing 15-plus years of old messages. 

>2) start over and restore the older C:\Pmail from backup? I'd lose the

new messages, which would be inconvenient, but not as much as losing

15-plus years of old messages.

Don't start over or try to restore all c:\pmail and below. We/You are only concerned with ..\mail and below and only part of that while being careful to *not* restore the files you do not want. Restore only the *.pmm and *.pmi from the backup and copy it to a temporary location on the current system. Then add that location using add mailbox to list function. Then you can read or copy messages to folder on the current install and username home mail box.

If restoring an old .pmm folde from archive  you could run RESTARCH.exe program to create new index also. You can pick that program up from Community downloads location. Read the built in help information part of the program.

Jerry, thanks for your reply, but I have another issue: The backups I thought I made seem to have let me down.

The external HD backup reports a PMI file created 9/28, but modified on 9/26 (?). The PMM backed-up file, though, was created & modified on 9/18 -- it's weeks old.  I cannot explain this;  I use PMail every day, and the backup program does a 'safe' copy and then a verify. It should have made a backup on 9/29.

Just to complicate matters, I also have a 'cloud' backup (SugarSync). The cloud version reports a PMI backup at 9/29/12 3:25:26 PM EST, but a PMM backup at 9/26/12 10:40:59 AM EST -- which is the file that PMail deleted. Prior to that the cloud has one stamped 9/25/12 12:54:26 PM EST. Again, I don't see why there isn't a later backup.

I can try using the PMI and a PMM that are closest to each other from backups, which will require me to undelete the 9/26 PMM file. What does RESTARCH.exe do, and can it help me here?

Note: I'm still at a loss to understand why Pegasus Mail deleted that folder TWICE:  when I installed the upgrade, and again when it encountered an indexing issue. This truly is aggravating.

Could an anti-virus program be an issue? Could be deleting due to a false positive.

I've had a client run into that similar condition (deleted .PMM file when PMail does a automatic recovery of deleted space).
If I've recalled correctly, the below info should help.
SugarSync is only going to backup the files if they have changed. Do not worry about the .PMI file.
Obtain the latest .PMM file and place someplace (not in the MAIL folder). Run the mbxmaint_ui.exe utility (found in the PMail\Programs directory) and Repair the .PMM file. The utility will rebuild a .PMI file to match that .PMM file. You may also want to consider having the utility Compact that same .PMM file.

If you get the .PMM file from SugarSync you may need to Take Ownership.
From an Administrator CMD prompt at that "someplace" directory:
takeown /f *.PMM /r /d y
Then overwrite the any existing copies of those two files with the "new" ones, appropriately renamed.

If you have any real-time antivirus software scanning the Pegasus Home mailbox directory, you may want to consider excluding that location.
Also if you have indexing service on the mailbox directory, you may want to consider disabling the service for that location.

For the client that had the afore mention condition I've also disabled PMails automatic folder compaction and employed a script to do so using the command line version mbxmaint.exe.
Since doing these changes, the problem has not reoccurred.

> Could an anti-virus program be an issue? Could be deleting due to a false positive.

Very unlikely. I've used AVG Free for a few years, and it plays nicely with PMail -- it targets and deletes individual messages.

[quote user="Guy"]

Do not worry about the .PMI file.

Obtain the latest .PMM file and place someplace (not in the MAIL folder). Run the mbxmaint_ui.exe utility (found in the PMail\Programs directory) and Repair the .PMM file. The utility will rebuild a .PMI file to match that .PMM file. You may also want to consider having the utility Compact that same .PMM file.

[/quote]

Well, that did the trick. I may have lost a few messages, but Old Mail is back -- and backed up in three places now. ;}  At 478 megs, it's easily my biggest folder. Perhaps that accounts for its deletion?

Another interesting thing: I fired up a GUI undelete program, and... the folder did not exist on the disk. (Nor in the Recycle Bin, not that I'd expect a DOS-deleted file to go there.)

Thanks to everyone for their suggestions and encouragement. ...Jerry, I couldn't even see your emails to me until I got Pegasus back up. (I didn't want to risk using it until all was well.)

So, I reduced the size of the folder from about 489 megs to 392 megs, and... PMail still deletes the folder if I delete more than about 100K worth of messages at one time.

I've taken to backing up OldMail between sessions so that when PMail deletes it, I can re-copy it and try again.

This is (obviously) not normal behavior, as there have been times -- under other versions -- when I've deleted a lot more than that without incident.  Has anyone replicated this?

I suggest you consider disabling the "Deleted space recovery" feature.

 Tools > Options... | General settings > Advanced settings
  Recovery of deleted space from folders
   Compact folders once [0] bytes are deleted [0=never]

Then either perform "Recover deleted space" manually via the Right-Click context menu option (after proactively backing up the folder), or perform the similar function via mbxmaint_ui.exe or scripted mbxmaint.exe command line utilities.