On Sep 12, 2006, at 1:43 PM, Tony Finch wrote:
On Tue, 12 Sep 2006, Joe Abley wrote:
I've seen many people use "." as part of MX RDATA to indicate that
a host should not receive mail (e.g. "PRINTER.EXAMPLE.COM. 3600 IN
MX 0 ."). I seem to remember that meaning is documented informally
in Cricket Liu's book, but I could be wrong about that (I don't
have a copy near the keyboard).
The "no service here" meaning of this kind of "." is explicitly
specified for SRV records. The specification for MX records is more
vague, but RFC 2821 does say "If MX records are present, but none
of them are usable, this situation MUST be reported as an error."
Even with the "." defined in the SRV record as "no target", there are
attempts to resolve "." hostnames. Using this "." syntax where a
local-part.hostname is expected, how often will "." be resolved? The
desire of this draft is to prevent extraneous. Could "localhost." be
used instead? Still no valid email-address can be generated, where
resolving localhost might not set a bad precedence.
-Doug
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