I'm running Windows Live Mail 2012, Build 16.4.3528.0331, under Windows 10 Pro.  Although no longer supported, I like this mail program.  I have it set for POP/SMTP operation for two email accounts, one Microsoft, one Google.  Both accounts are set up through their respective Web utilities for POP/SMTP fetch/send also.

Everything works fine, has been for years now, but these accounts are acting more like IMAP than POP/SMTP.  It was always my understanding that POP simply downloaded mail when asked, and would even delete it from the server upon successful download if asked to do so.  What I'm finding, however, is a sort of 'synchronization' between my PC and the email accounts.

If, for example, I download mail from one of these servers while the Webmail utility for the account is open in my browser, I see the mail transferred and deleted from the server.  Then I look at download mail on my PC and either delete items or put them in the Junk folder... on my computer, that is.  Then the next time the PC communicates with the mail server those messages mysteriously appear in the Webmail Trash and Junk folders as seen through my browser.  In other words, my computer is telling the MS and Google servers what was done locally with those messages on the machine, and Windows Live Mail is either kicking them back to similar folders in MS and Google servers, or duplicates are being placed in the server's folders.

Is my understanding of POP/SMTP off-base, or is something strange going on here?