Tony Finch wrote:
> John C Klensin <john-i...@jck.com> wrote:
>> IN MX 0 .
>>
>> At least in the near term, some SMTP Server ("MTA")
>> implementations will conform to that rule (many already use it)
>> and some won't. For the latter, they will presumably do what
>> the SMTP specs say to do. In summary, that is to look up the
>> address(es) associated with the root and try to open a mail
>> connection to one of them.
>
> There are no addresses associated with the root, so the mail server will
> immediately report a delivery error. RFC 5321 section 5.1 paragraph 2
> final sentence.
>
> The SMTP server will not try to connect to the root name servers, as your
> message suggested.
true as stated.
what's unstated here is that every SMTP sender who encounters such an MX
without understanding its new meaning will do two or three lookups: ".
MX", [". AAAA",] and ". A". if they are behind an RDNS that doesn't do
negative caching (and there are many, though none of them are open
source; the open source RDNS servers do negative caching right) then
these two or three queries will flow through to the authority servers
for "." which is to say the root name servers.
the long tail on old interpretation is between one and three decades.
(which is also why repurposing/redefining things like TCP/53 is
unworkable, as discussed separately.)
if IETF had rules, one of them should be, don't redefine things that are
in an existing datapath -- make a new datapath.
vixie
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