This question often comes up in Google, so I decided to add an important note.
Don’t ever use X-Auto-Response-Suppress in your filters as suggested in the other answer.
X-Auto-Response-Suppress is used by Exchange to tell other servers to not send auto-replies in response to an email. It doesn’t mean that this email is an auto-response.
We had to learn it the hard way, hope you won’t have to. I’ve also wrote a blog post with more details: http://www.jitbit.com/maxblog/18-detecting-outlook-autoreplyout-of-office-emails-and-x-auto-response-suppress-header/