Outlook 2003 receipt problem

A user requests an alert that an email message was read/delivered.

Whats it mean when the user is still getting an alert that the message was read when the recipient was out of the office that day, and has no remote access?

Intruder? Virus? Obviously a security issue. I have not had a chance to dig into the details yet. Just trying to get my ducks in a row first. I never herd of this before.

Thank You