Joe gets emails from his brother and vice versa telling them to go to another site. Leo says that's a phishing scam using spam to do it. It's likely that the return address has been spoofed. We've seen this happen often with users of Yahoo mail.
ScooterX in the chatroom says that whoever clicks on the link in the email sends the same email to others in their contact list. So it may be that both have clicked on that link and sent it out.