you'll need to clear up something for me.
You say that your computer is "....configured for my email addresses and OE on my wife's PC for her email addresses". I'm not quite clear about what you mean by that.
If you have an ADSL connection via BT in your name you'll have a POP3 mail box, and that will be in your name too. Email addressed to: [email protected] will be collected by your copy of Outlook Express whenever you do a send and receive on your machine.
It sounds as if you're saying that your wife has a completely separate POP3 mailbox on the mail.btinternet.com server, and that she's randomly getting some of your mail in her inbox in error - is that a correct assessment of what's happening?
If it is, it's strange, and very unusual. Email addresses are unique, and for one person to receive another's mail is a rare (but not unheard of) occurrence.