Windows Mail & Yahoo + INBOX

My email arrives via Yahoo first, and then to windows Mail, but when I delete email from windows mail (holding shift key & delete, so that it is deleted forever), and save some emails to a different folder, so that my inbox is empty, if I logon to yahoo it still shows all my emails in the Yahoo mail inbox.
When I used to launch Windows Mail and all my emails arrive, then go to Yahoo inbox, it would of cause be empty, but as above over the weekend something has happened, any clues?
Now I am having to delete from Windows Mail & Yahoo!!!
Your thoughts are most appreciated

Dieselman: Thanks for that, wherever I am in the world I access my emails via Yahoo, but have always since Vista & now Windows 7 have used Windows Mail, not really into cloud base at the moment, but I know one day we will all have to succumb.

The account should be set up as POP3 and the option to "leave a copy of mail on server" should not be checked. (Also, doesn't Yahoo charge a fee for POP access?)

roncerr: Cheers for the input, don't know about a charge for pop access, but have just unchecked " leave a copy on on server" and hope that works.:)

It has worked, thank you very much. now resolved.