The only part of an email you can trust are the headers you or your ISP add when it arrives, which is going to be something like :

    Received: from farlep.net (unknown [89.105.247.162])
        by mail.techiferous.net (Postfix) with ESMTP id B1E30EC456E
        for <info@techiferous.net>; Fri, 14 May 2010 10:24:22 +0100 (BST)

everything else - especially the RCPT TO, MAIL FROM, From: and To: cannot be trusted (unless the message is signed etc.).

I administer the mail for 10k domains, finding 1 spammer and doing something about it is hard work.

Spamassassin, SPF, DKIM are all good tools against SPAM, I can recommend using them all in combination; 90% of all our incoming mail is refused / tagged in this way.

I would review your assumptions too :

    % host discokenny.com
    Host discokenny.com not found: 2(SERVFAIL)

If they tried to send it to me, I'd never even know.