The missing FROM: thing is from some years ago. That is information only, and isn't what is causing your problem.
David's suggestion to update is probably a good one (see
http://pmmail.os2voice.org/index.php?title=PMMail_for_OS/2, for more information), Be sure to do the required YUM updates. Do that before installing, if you can, but I suspect that there is some other problem that is causing the re-index problem.
You can get to the PMMail Mantis Bug Tracker using Help-> VOICE on the web-> PMMail technical Support. Log in or sign up for a new account. If you open an incident, be sure to include verbose logs, and a detailed description of the problem, along with any other information that may prove to be useful,
Be assured, that your messages are probably safe, From what you say, something is causing a re-index to fail, which is simply the generated message index. PMMail 3.25.00.1993 (32809) - Jul 25 2021 16:20:17 +0000 (GMT) may (or may not) fix the problem, but it would be the first thing to try. You may want to BACK UP, so you can get back to where you started. Often, simply doing Re-Index again will get past whatever it doesn't like (especially if you haven't done a Re-Index recently, which would seem to be the case since you don't know about the FROM: thing), I have also seen stray, non message, files get put into the folders, and that can cause problems.
Did you, by any chance, install the libc, and libcx, updates from the netlabs-exp repository? I haven't seen any problems with that, but they are new, and probably not well tested.