Its definitely the HELO/EHLO that is the issue, as Alphaphi stated:
Oct 7 01:09:23 z1 postfix/smtpd: NOQUEUE: reject: RCPT from S010600173fbe827d.ek.shawcable.net[126.96.36.199]: 504 5.5.2 <Kays>: Helo command rejected: need fully-qualified hostname; from=<email@example.com> to=<firstname.lastname@example.org> proto=ESMTP helo=<Kays>
It is either a spammer, or misconfigured. If this is someone you want to be receiving mail from, advise them to have their FQDN set correctly for their MTA. There are occasionally vendors that my college does business with who have this screwed up. Its not something you want to worry about changing on your end or whitelisting.
State University of New York at New Paltz