On Thu, Aug 05, 2004 at 04:22:36PM -0700,
Lou Katz <lou(_at_)metron(_dot_)com> wrote
a message of 41 lines which said:
??? I thought it was the other way around - that only A-Z,0-9 and
'-' were valid for DOMAINS (or haven't I had enough caffiene?) but
other chars could be used for hosts.
Not at all. Sorry, but you are wrong.
The rules for *domains* are:
RFC 1035, 3.1. Name space definitions
RFC 2181, 11. Name syntax
Both say that almost any character can be used in in *domain* name.
But the rules are much stricter for *hosts*:
RFC 113, 2.1 Host Names and Numbers
They allow only LDH (not even US-ASCII), Letters, Digits and Hyphen
and this restriction is embedded in a lot of programs and
libraries. (Sidenote: this is the rationale behind the Punycode
encoding, see RFC 3490 and 3492, of Unicode domain names.)
That's why underscores are used for domains without hosts like in SRV
records (RFC 2782) such as _tcp (or _spf, which should have been used
for SPF).
PS: why in hell the spf.pobox.com site continues to refer to "SPF RFC"
in many places? Marketing lie or lazyness in naming?