The problem is solved! A great thanks to everyone for all the valuable information and suggestions you offered. I learned quite a bit, especially about talking to the dovecot server using the telnet/openssl suggestions and the available POP3 commands.

Many of you were correct about your diagnosis, but I had some things happening that were creating confusion. Here is a brief summary of what I discovered.

There were a few initial dovecot configuration issues which I eventually ironed out and, as I was reporting at the end of last week, the diagnostic logs seemed to indicate that the connection was successful. Yes, it turned out that Outlook was indeed set to leave a copy of the emails on the server for two weeks -- a setting hidden away on a sub-menu. Now, why this did not seem to be the case was because every time Outlook connected to the Solaris system to retrieve mail, all the messages were immediately deleted (despite this setting), so I was expecting the same behavior on the Linux machine and wasn't looking for the setting. There is something different about how the pop3 handler is working on the two systems.

The second problem, which some of you guessed, was that the emails left on the server were not being downloaded because when I wasn't looking, Outlook had already downloaded and tagged them. So, even when I thought there was new mail (new to me anyway) in the inbox, Outlook had beaten me to them so that when I looked, I could see no new mail flowing over to the Windows machine. Disabling the retention setting removed the ambiguity and now I see any new mail in the inbox moving to the other system.

Thanks again to everyone!

Jeff