Sendmail and local addresses

[Jason Majors <jason@whizzird.net>]

I have several machines, one acts as a mailserver, with an MX entry and all.
The others are clients that know to use the server as a smarthost. When I send
mail to a local account, I get an error from the smarthost server saying that
the address user@box.whizzird.net can't be found. But when I add the
@whizzird.net to the address it works fine. These boxes are running the sendmail
from testing (the one from stable stopped working on me).
I tried to use the sendmail address rewriting mini-HOWTO's advice to allow it
to send local mail, but the sendmail I have doesn't like the format of the file
for some reason. Is there an easy way to send local mail with sendmail?

Thanks,
Jason