Use of SRV Records for Locating Email Submission/Access Services
RFC 6186

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• IESG evaluation record
• IESG writeups
• Email expansions
• History

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• 05

Internet Engineering Task Force (IETF)                          C. Daboo
Request for Comments: 6186                                    Apple Inc.
Updates: 1939, 3501                                           March 2011
Category: Standards Track
ISSN: 2070-1721

    Use of SRV Records for Locating Email Submission/Access Services

Abstract

   This specification describes how SRV records can be used to locate
   email services.

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/rfc6186.

Copyright Notice

   Copyright (c) 2011 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.

Daboo                        Standards Track                    [Page 1]
RFC 6186                      SRV for Email                   March 2011

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 2
   2.  Conventions Used in This Document . . . . . . . . . . . . . . . 3
   3.  SRV Service Labels  . . . . . . . . . . . . . . . . . . . . . . 3
     3.1.  Email Submission  . . . . . . . . . . . . . . . . . . . . . 3
     3.2.  IMAP  . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
     3.3.  POP3  . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
     3.4.  Priority for Domain Preferences . . . . . . . . . . . . . . 4
   4.  Guidance for MUAs . . . . . . . . . . . . . . . . . . . . . . . 5
   5.  Guidance for Service Providers  . . . . . . . . . . . . . . . . 6
   6.  Security Considerations . . . . . . . . . . . . . . . . . . . . 7
   7.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 7
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 8
     8.1.  Normative References  . . . . . . . . . . . . . . . . . . . 8
     8.2.  Informative References  . . . . . . . . . . . . . . . . . . 8

1.  Introduction

   Internet email protocols include SMTP [RFC5321], IMAP [RFC3501], and
   POP3 [RFC1939].  IMAP and POP3 are both message store access
   protocols used by message store user agents (MUAs) to manipulate
   email messages after delivery.  [RFC4409] defines a "profile" of the
   SMTP service that is specifically used for message submission.  MUAs
   are expected to submit messages to mail submission agents (MSAs)
   using this approach.

   [RFC2782] defines a DNS-based service discovery protocol that has
   been widely adopted as a means of locating particular services within
   a local area network and beyond, using DNS SRV resource records
   (RRs).

   [RFC5321] specifies how to use DNS MX RRs to locate SMTP services for
   a domain.  However, MUAs are expected to use the submission protocol
   defined in [RFC4409], which does not use MX records.

   Typically MUAs have required users to enter a fully qualified domain
   name (FQDN) and port information for the services they need.  This is
   not ideal as the way in which server configuration information is
   specified can differ from MUA to MUA, and can be confusing to users,
   leading to errors when inputting the details.  Alternatively, some
   MUAs have adopted a complex "auto-discovery" process involving
   probing a domain to see what services might be available.  A better
   approach to all this would be to require minimal information to be
   entered by a user that would result in automatic configuration of
   appropriate services for that user.  The minimal information entered
   would be the user's email address.

Daboo                        Standards Track                    [Page 2]
RFC 6186                      SRV for Email                   March 2011

   This specification defines new SRV service types for the message
   submission, IMAP, and POP3 services, to enable simple auto-
   configuration of MUAs.  The priority field of the SRV record can also
   be used to indicate a preference for one message store access
   protocol over another.

2.  Conventions Used in This Document