As I said, the suggestions about lock files were key.
It guided our investigation until we found the real
problem. I thank everyone who responded.
I've seen other posting about corruption of the From
line. Perhaps you have the same problem.
I had the exact same problem with my upgraded OpenLinux system.
For the record, if you are running the imapd that comes with it, you should
really set your permissions for the directory is as follows:
chmod 1777 /var/mail/spool
I got that feedback from the guy who wrote imapd, and it works very well.