I run Outlook on a desktop and laptop. Both are set to save messages on
server. I consider the desktop the "master" and periodically I want to
copy its PST file to the laptop. However when I do, the next time I
receive on the laptop I re-download huge numbers of message (everything
still on the server perhaps?) and end up with a huge duplicate problem.

What can I do about this? And how does the unseen-message info work,
anyway?

TIA for any advice...