It appears to me that you want to set up a "catch-all" e-mail account.
You'll could look into using a
virtualusertable seeing as you're using Sendmail.
Search google and the sendmail site for "catch all" and "virtualusertable" and you should find the information required to implement this.
Personally, I'd say if somebody sends e-mail to a non-existent address and it's bounced back, then that's a GoodThing(TM). At least that way the original sender knows they've hit a non existent mailbox, and would (if they're savvy) e-mail the postmaster (which'd probably end up being aliased to root anyway) asking for the correct e-mail address. My 2p....
BTW - Moxxx - Mutt is just a mail client. You cannot use Mutt for configuring sendmail! Mutt reads your e-mail, and lets you compose messages, reply, etc. Sendmail is a MTA, mutt definitely is not!
Cheers
ZB