sendmail and local mail

How do I keep sendmail from adding my MASQUERADE_AS name to my mail that is to be delivered locally? For any outgoing mail, I want to masquerade as my ISP, but not the mail that stays local to my system... I've rebuilt my sendmail.cf from the /etc/mail/linux.mc file and I have checked options that seem to be relevant to those in my sendmail.mc file from my redhat configuration, but that didn't do anything for me Thanks! -Michael