If you receive an SMTP error or bounce message containing the text string

UP Email not accepted for policy reasons. Please visit http://help.yahoo.com/help/us/mail/defer/defer-04.html

there is something about the message contents that Yahoo! Mail will not accept for policy reasons. For instance, it is against Yahoo! Mail's policy to send phishing/fraud attempts or viruses. If you feel you have received this error for a message that should be accepted, we encourage you to provide us with detailed information about the rejected message.