HDR From: The Post Office <postmaster>
HDR Sender:	mailer-daemon
SUB Subject: You can't use "localhost" as a hostname

The valid addresses for users on this machine are:

	{ai,cs,na,theory}.{toronto.edu,utoronto.ca},
	utai.uucp
	utorant.bitnet

You might try one of those instead of just "localhost".  Your message is
being returned unprocessed.