There are two steps to completely screwing yourself.  Please do both.

1)  ISPs regularly update their POP server names.   Change your POP server name in an existing mail profile to the latest one your ISP has.    Windows Live Mail will conveniently re-download ALL of your messages again,  so your inbox will be polluted with duplicates of every single message.

2)  Decide to rectify the above abysmal situation by deleting all your messages and then your mail profile.  Since POP servers maintain all the messages on the server, when you recreate your mail profile they should all be downloaded again.  Then you will have a sane single copy of each.

If you have followed these steps correctly,  ALL of your emails (perhaps several years worth, as mine were) will be irrevocably deleted from the mail server and your life, never to be seen again.  The deletion of messages on WLM,  for a POP server (!), is silently synchronized to that server.

After this happened I combed through the options to see if there was ANY indication that deletions were synchronized for a POP server, and if it is there I couldn't find it.   My guess is that they changed this behavior when they introduced IMAP support (since those are always synchronized).  

If only I had know... had known... had known...