Hotmail/Outlook eMail Messages deleted off of iPhone are not being delted off of server

I am using the MAIL app on my iPhone to acces my Hotmail/Outlook account. It is set up as a POP3 account. When I delete an email message on the phone, it is never deleted on the server, even though I have the settings in my phone set to delete them from server when removed from Inbox.

I have not found a clear answer to this issue. Right now I have 10K email messages when I log into my Hotmail