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Re: [apps-discuss] Last Call: <draft-ietf-appsawg-nullmx-05.txt> (A NULL MX Resource Record for Domains that Accept No Mail) to Proposed Standard

2014-07-18 05:54:17
Nico Williams <nico(_at_)cryptonector(_dot_)com> wrote:

I think what you're objecting to is the section 4.3 and related text
that conflates "does not accept e-mail" with "does not send e-mail".

Section 4.3 describes what is already done by existing implementations of
this spec.

Exim in its default configuration validates the domain part of email
addresses and will reject mail if the sending domain does not exist or if
its MX records point to nonexistent hosts. Exim also recognizes null MX
records and suppresses the target A and AAAA lookups and treats the domain
as invalid. However the null MX logic is just an optimization: Exim's
validation logic would get the same result if it tried to do the A and
AAAA lookups and found that . does not have any addresses.

Postfix does the same if you use the reject_unknown_sender_domain option.

There are good reasons for rejecting mail from invalid domains, e.g.
because you would not be able to send a delivery failure report.

Tony.
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