A "Null MX" No Service Resource Record for Domains That Accept No Mail
RFC 7505
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RFC - Proposed Standard
(June 2015; No errata)
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Last updated |
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2015-10-14
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Replaces |
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draft-delany-nullmx
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IETF
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Submitted to IESG for Publication
(wg milestone:
Jun 2014 - Publication requeste...
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Document shepherd |
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Dave Crocker
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Show
(last changed 2014-07-06)
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RFC 7505 (Proposed Standard)
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Yes
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Barry Leiba
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RFC-Ed-Ack
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Internet Engineering Task Force (IETF) J. Levine
Request for Comments: 7505 Taughannock Networks
Category: Standards Track M. Delany
ISSN: 2070-1721 Apple Inc.
June 2015
A "Null MX" No Service Resource Record for Domains That Accept No Mail
Abstract
Internet mail determines the address of a receiving server through
the DNS, first by looking for an MX record and then by looking for an
A/AAAA record as a fallback. Unfortunately, this means that the
A/AAAA record is taken to be mail server address even when that
address does not accept mail. The No Service MX RR, informally
called "null MX", formalizes the existing mechanism by which a domain
announces that it accepts no mail, without having to provide a mail
server; this permits significant operational efficiencies.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc7505.
Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Levine & Delany Standards Track [Page 1]
RFC 7505 Null MX June 2015
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions Used in This Document . . . . . . . . . . . . . . 2
3. MX Resource Records Specifying Null MX . . . . . . . . . . . 3
4. Effects of Null MX . . . . . . . . . . . . . . . . . . . . . 3
4.1. SMTP Server Benefits . . . . . . . . . . . . . . . . . . 3
4.2. Sending Mail from Domains That Publish Null MX . . . . . 4
5. Security Considerations . . . . . . . . . . . . . . . . . . . 4
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
7.1. Normative References . . . . . . . . . . . . . . . . . . 5
7.2. Informative References . . . . . . . . . . . . . . . . . 6
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction
This document defines the No Service MX, informally called "null MX",
as a simple mechanism by which a domain can indicate that it does not
accept email.
SMTP clients have a prescribed sequence for identifying a server that
accepts email for a domain. Section 5 of [RFC5321] covers this in
detail; in essence, the SMTP client first looks up a DNS MX RR, and,
if that is not found, it falls back to looking up a DNS A or AAAA RR.
Hence, this overloads a DNS record (that has a different primary
mission) with an email service semantic.
If a domain has no MX records, senders will attempt to deliver mail
to the hosts at the addresses in the domain's A or AAAA records. If
there are no SMTP listeners at the A/AAAA addresses, message delivery
will be attempted repeatedly for a long period, typically a week,
before the sending Mail Transfer Agent (MTA) gives up. This will
delay notification to the sender in the case of misdirected mail and
will consume resources at the sender.
This document defines a null MX that will cause all mail delivery
attempts to a domain to fail immediately, without requiring domains
to create SMTP listeners dedicated to preventing delivery attempts.
2. Conventions Used in This Document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
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