In the file /usr/lib/mh/mtstailor, the last line looks like this:
servers: localhost \01localnet
Dan Yocum also reports that sendmail on the local machine is configured in
such a way that it will not relay mail (a rudimentary method to thwart
spammers from using your machine as a relay point).
You should change the line to look like this:
servers: fnal.fnal.gov \01localnet
or whatever your local mail server is.
Dan Yocum & Connie Sieh