Hi eager beaver! Hadn't abandoned you but been up to my neck in hard disk cloning and rescuing data. Got to the end of the tunnel and I'm a happy bunny again - thanks to Partition Magic 6.0.
Now, you're correct that if you never leave e-mails on the server you will not have a problem with duplicates if you retrieve using a clean version of OE. However, a POP3 record is always created and updated when you start from scratch.
No, compacting OE folders is not the same as emptying your Recycling Bin. For some reason, even when you delete e-mails from a Folder, the substance of the e-mail remains in the appropriate File - until, that is, you "Compact" the Folder. In this respect, it's a bit like deleting a File from a disk. The contents of the file remain on the disk until they are over-written; only the File name is deleted from the Table of Contents.
I did an experiment to illustrate this:
My Deleted folder was "Empty"; the associated File (Deleted.dbx) was 187Kb.
I then compacted the Deleted Folder in OE; the File size reduced to 59kB. That is the default size of any empty Folder in OE 5.5.
So it's a useful thing to know this because, if you have received any e-mails containing viruses or unsavoury stuff, simply deleting them and emptying your Deleted Folder doesn't get rid of them. Even compacting the Folder doesn't remove traces of them from your Hard Disk but it's a help.
This way lies madness! Check the size of your Files in the Identity Folder.