Bill Cole wrote:
Lyndon Nerenberg wrote, On 6/16/09 9:55 PM:
On Tue, 2009-06-16 at 17:24 -0700, Douglas Otis wrote:
IMHO, all outbound MTAs should be required to return CVS records for
their EHLO name and offer MX records for their inbound.
Doug, are you sure that's what you meant to say? The sentence is a bit
ambiguous. Are you really saying any host that sends mail (is an SMTP
client) MUST also host an listed SMTP server?
I can't testify to what he meant, but I think what he is actually saying
is that if you have a machine that says "EHLO some.name" then there
should be both a MX record for some.name and a SRV record for
_client._smtp.some.name (i.e. a CSV/CSA record).
However, the standard requires that it says "EHLO host-at.some.name".
It is a seemingly simple task to drop the leftmost label(s) so as to
obtain the mail domain, but doing that properly requires a zone cut
algorithm that most servers miss.
That doesn't mean requiring inbound SMTP on every outbound, it means
requiring an affirmation in DNS that a name can be used in EHLO by a
particular IP address and a way to get mail to the responsible party for
the machine(s) using that name in EHLO. This is an admirable goal. A
weaker goal would be to get people running non-spamming mail servers to
follow the existing accepted standard of using a valid resolvable FQDN
in EHLO.
If we have a weaker goal and an admirable one, we're better off if
they don't conflict with each other. We cannot ask for a domain name
after EHLO, except for tiny ESPs whose domain name, host name, and IP
address are the same thing. If we need the domain name, we can either
mandate the zone cut algorithm, or use a different verb than EHLO.
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