On Jun 9, 2007, at 10:48 AM, Hector Santos wrote:
Jeff Macdonald wrote:
On Sat, Jun 09, 2007 at 07:51:51AM -0700, Douglas Otis wrote:
The discovery process itself might provide a solution. For a
message to contain a valid email-address, the domain of this
address MUST locate either an MX or A record. The DKIM WG could
strongly recommend A record discovery be deprecated, and that
only MX records be used for discovery. Within a few years, it
should be possible to obsolete use of A record discovery. An
email-address would not be valid without an MX record. This
would mean that policy placement adjacent to the MX record would
be the only location any policy record would need to exist. In
this case, the discovery process itself indicates whether or not
the sub-domain is USED/UNUSED.
Are you referring to the process that some MTAs follow? For
example, if
a MTA needs to deliver a message, it is suppose to find a MX for the
right hand side of the email address and deliver it to the eventual A
record (Hector's claim that some MX records return IPs confused me).
I was referring to MX expansion and how each DNS client within a
SMTP client may behave. More below.
Some MTAs, when they don't find an MX record, just lookup an A record
instead and deliver to the resulting IP.
If that's the case, shouldn't the deprecating of A lookups when a MX
lookup fails be brought to the SMTP group?
Yup, and IMO, I can almost guaranteed the idea will be killed
ASAP. I would vote against it.
I seriously doubt people will begin to screw around with their
various retries logic. Plus, you are going to hear those who say
MX is about inbound, not outbound and "Never The Twain Shall Meet."
This is not about using MX records as a means to resolve an outbound
path. This is only about confirming the domain used in an email-
address simply exists. Existence is determined by the mere existence
of records used to discover the inbound path for the email-address.
This does not require that inbound and outbound servers be one-in-the-
same.
"Proof of use" would not require that any IP address match that of
the SMTP client, or that the email-address domain associated with an
MX also provide an A record, or that an A record actually locate an
SMTP server.
-Doug
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