OK, folks, here's the next chapter.  I went into my POP3 settings and unchecked the "Delete mail on server after it has been successfully retrieved" and changed the "Default action for messages still present after filtering" from "Download" to "Leave on server".  I have an XP machine and did NOT reboot, which may explain the following behavior:  I opened Pegasus and found that two messages, regardless of these settings, automatically downloaded to my New Messages folder.  I then clicked "Selective mail download" and found those two messages AND a test email from my brother on the server.  My explanation for this is that while the Pegasus settings did not reset (because I hadn't rebooted) the mail server did in fact do as I had asked -- and the messages stayed on the server.  The reason that only two messages automatically were downloaded rather than THREE was that Pegasus again "ate" the copy of my brother's email that was downloaded.  I have confirmed that all messages are still on the mail server.  Next step is to reboot the computer to see if the automatic download will stop.

I still have no idea why Pegasus is eating those messages from my brother, but at least I know that the server is retaining them. 

I do NOT get this.  I have been a Pegasus user since before V4 came out, and am currently using v4.63.  For some reason I NEVER receive emails my brother sends to me.  They never appear in my New Mail or my Deleted Messages folders.  When he sends one, it appears on my Android phone (yes, it's set up to monitor but NOT to download mail from my mail server) but not in my Pegasus installation.  I don't appear to have this problem with any other sender.

My quest to figure this out (a bunch of years doing computer tech support) has led me to even change ISPs, figuring that the email was getting lost in the bowels of their mega-corporate servers, but this had absolutely no effect on the problem.  I cannot see how an email could be downloaded to my system but never be seen.  I KNOW my filters aren't doing it, because they simply rout stuff I don't want to Deleted Messages.  His email address is in my whitelist, for what it's worth.  How can stuff sent to me get deleted without me seeing it?  My email address has not changed for more than 10 years, so I know the email is addressed correctly, and this problem only appeared less than a year ago, so it just doesn't make sense.  Anybody have any ideas?

No idea what's happening, but perhaps you could have Pegasus do about the same as your Android phone, i.e. monitor the email. So, instead of downloading it, you could try File, Selective download and see what happens then.

Thanks, Steffan -- I'll try doing that and report back.  That way I can be sure the email is at least regularly appearing on the mail server.  I have tried looking there before using Pegasus to download, and gotten inconsistent results (worked once, didn't work once).  If I can consistently see the emails from him on the server, I have at least one more link in the chain confirmed, and will be even more certain that my Pegasus installation is at fault.  Is there any chance that the sheer volume of email I have stored could somehow affect this one user?  I surely cannot understand how -- but I'll try anything!

Lance

OK, I figured it out.  Yes, it was something I did (Mea Culpa).  It was the Address Gathering "feature".  I had put my brother's address in as one of the addresses attached to a folder, and then have not reopened that folder.  A folder search turned up ALL of those "missing" emails.  Dumb mistake, I know.  I just did not understand the effect of setting up autofiltering in a folder.