The messages in WebMail that are in the trash
will get downloaded into Outlook (and other POP3 clients) unless they
are actually purged from WebMail.
Like the Windows or Mac trashbin, the WebMail trash is a temporary
holding place for information that is to be purged later. Since the
messages are still considered "live", they get downloaded along with the
rest of the mail when you login with a POP3 client.
To purge the messages from the trash in WebMail, navigate to the WebMail trash, then click the Purge button.