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Re: Do domains in SMTP have to exist ?

2008-04-12 13:51:56

At 09:23 12-04-2008, John Levine wrote:
Over in DKIM land there is a battle going on with respect to the
treatment of domains that don't exist, with "don't exist" meaning
something like an authoritative DNS server doesn't return an MX or A
or AAAA or CNAME for the name.

I'm answering from a RFC 2821bis perspective. Section 5.1 of draft-09 mentions how to locate the target host. If the authoritative DNS server returns a NXDOMAIN, the message would be returned as undeliverable.

Looking through the current draft, it looks to me like everyone
assumes that domain names have to exist, with the explicit exception
of the HELO/EHLO name, but it never says so in so many words.

The current draft focuses on how to find a path to deliver the message. Even if the domain exists, it doesn't necessary imply that the message can be delivered, for example if we have an IPv4 client trying to reach an IPv6 only. Section 5.2 mentions that.

Is this a deliberate omission, or is it so obvious that it wasn't
worth stating explicitly?

Section 2.3.5 discusses about domain names. A domain name, used in RCPT TO:, which does not fit that description will result in delivery failure.

PS: The domains in the DKIM discussion are 2822 domains, but the
2822upd draft punts the interpretation of domain names over here.

If the domain part of the addr-spec is used to convey addressing information for SMTP, it has to conform to its specifications.