[RFC-3834](http://tools.ietf.org/html/rfc3834#section-5) has been referred to by many people trying to solve this problem. it says `Auto-Submitted` can have possible values as `auto-replied` (which you've covered), `auto-generated` and `no`. [there's a suggestion](http://stackoverflow.com/questions/9426801/detect-auto-reply-emails-programatically) to ignore any other response than `no` to detect human responses. should we update our logic to reflect that ?