I wouldn't have put in auto-submitted except that some uniform means
of marking automatic responses is necessary to prevent loops. There
are heuristics that could be used instead, but they don't work as well.
Using a MAIL FROM of <> for autoresponses meets the requirement to
prevent loops. Auto-submitted is only useful (to meet the 'prevent
loops' requirement) when the MAIL FROM isn't null. For other reasons
there is some additional value in including auto-submitted even if
MAIL FROM is <>.
-d