email addresses like erik.quanstrom@coraid.com were not being flagged
as nonexistant because they are invalid.  example of the problem

cpu% telnet net!ladd!smtp
connected to net!ladd!smtp on /net/tcp/30
220 quanstro.net ESMTP
HELO ladd.quanstro.net
250 quanstro.net you are ladd.quanstro.net
rcpt To: <bilbo@quanstro.net>
250 2.0.0 receiver is quanstro.net!bilbo.baggins