To LinuxBender: RFC2549 also clarified the key words:
MUST Usually.
MUST NOT Usually not.
SHOULD Only when Marketing insists.
MAY Only if it doesn't cost extra.
RFC2142 - I like it when organisations use standardised email addresses such as support@ and security@ for different business units.
Unfortunately many orgs either don't have these mailboxes set up, or they aren't actively monitored.
RFC-6919 [1] The key words "MUST (BUT WE KNOW YOU WON'T)", "SHOULD CONSIDER", "REALLY SHOULD NOT", "OUGHT TO", "WOULD PROBABLY", "MAY WISH TO", "COULD", "POSSIBLE", and "MIGHT" in this document are to be interpreted as described in RFC 6919.
I'm working on writing a paper for a class on the DNS system. I really like rfc1035 [1]. It describes the goals, and terms involved. Also it goes into details on their design tradeoffs, and how they made it distributed.