On Fri, Jul 18, 2014 at 02:18:58PM -0700, ned+ietf@xxxxxxxxxxxxxxxxx wrote:
> > The point of null MX records it to explicitly say the address is invalid,
> > so an address status would seem to make sense.
>
> No, the point is to say that a host is invalid.
A recipient domain is (often) not a host. The lookup key for a
nullmx RR is a domain. Since no MX hosts are returned, what is
invalid is the recipient domain, which is part of the recipient
address. I generally also have mappings in the Postfix transport
table of the form:
.invalid error:5.1.2 invalid destination domain
and rewrite unqualified mailboxes in headers from remote clients
by appending "@domain.invalid".
http://www.postfix.org/postconf.5.html#remote_header_rewrite_domain
The text in 3463 is quite broad:
X.1.2 Bad destination system address
The destination system specified in the address does not exist
or is incapable of accepting mail. For Internet mail names,
this means the address portion to the right of the "@" is
invalid for mail. This code is only useful for permanent
failures.
It applies equally well to nullmx and the "invalid" TLD.
--
Viktor.