Post the email. It is extremely unlikely that Yahoo sent it. It is more likely a spoof, an email that looks as though it is official but is sent by a private party.
This is a legitimate and real e-mail message from Yahoo!. I received one myself for writing a negative review about Brokeback Mountain. I just didn't like the movie. I gave it a "D". The problem is, and it's a problem with Yahoo, if you offend someone, for whatever reason, that person can report the post as abuse. You can do it also. When you go to the message board for Brokeback Mountain, and then you read a message, there is a "link" on the left that says "Report Abuse". All you have to do is click this, a new screen will pop up. You fill in you e-mail address and why the message offended you. Click "SEND", and in a few hours, the person who wrote that message (or Post) will receive the identical e-mail from Yahoo stating they have violated their agreement with Yahoo. It's that simple. Anyone (Yahoo Users Only) can do it.
So, go to the message area in the Brokeback Mountain movie reviews, and read the messages. If one offends you, click "report abuse". I think you will find many messages there that will offend you. If a person receives many reports of abuse, their account will be terminated...so use this feature freely.