i have not set up the email section yet so this is a shot in the dark. i am not sure if you can schedule a task to look at the contents of the email and then discard ones that have that autoresponse text in them.. i am pretty sure you can
if not.. then possibly use something like this :
http://www.CheapSpamKiller.com
it is a spam filtering thing. it does not interfeer with your email at all and it can check multiple accounts (i have it checking 26 accounts on several domains). if you have one that is from a certain customer that is always an auto responder, you can set up rules to test and then delete it.