sendmail autoresponder

[Dave]

Hello,
    I've got a box that i took over that runs sendmail, mailscanner, and sa 
for antispam. There's an email address at one of the domains that the owner 
has indicated he would like an autoresponder hooked to it. THe objective is 
whenever someone sends to that address it won't be delivered to a mailbox, 
but dropped and the autoresponder msg will be sent back. I'm a sendmail 
newbie in the extreme and would appreciate any advice.
Thanks.
Dave.