Facsimile Using Internet Mail (IFAX) Service of ENUM
RFC 4143

Document Type RFC - Proposed Standard (November 2005; Errata)
Updated by RFC 6118
Authors Kiyoshi Toyoda  , Dave Crocker 
Last updated 2020-01-21
Stream IETF
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IESG IESG state RFC 4143 (Proposed Standard)
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Network Working Group                                          K. Toyoda
Request for Comments: 4143                                           PCC
Category: Standards Track                                     D. Crocker
                                                           November 2005

          Facsimile Using Internet Mail (IFAX) Service of ENUM

Status of This Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2005).


   This document describes the functional specification and definition
   of the ENUM Naming Authority Pointer (NAPTR) record for IFax service.
   IFax is "facsimile using Internet mail".  For this use, the Domain
   Name System (DNS) returns the email address of the referenced IFax
   system.  This mechanism allows email-based fax communication to use
   telephone numbers instead of requiring the sender to already know the
   recipient email address.

1.   Functional Specification

   An IFax client makes a [ENUMbis] DNS query, using the target system's
   telephone number.  The returned NAPTR record specifies an email
   address to be used for reaching the target system.  The email address
   is then used in accordance with Simple Mode of Facsimile using
   Internet Mail [RFC3965], Extended Facsimile using Internet Mail
   [RFC2532], or Full Mode Fax Profile for Internet Mail [FFPIM] is

   The key words "MUST", "MUST NOT", "SHOULD", "SHOULD NOT", and "MAY"
   in this document are to be interpreted as defined in "Key words for
   use in RFCs to Indicate Requirement Levels" [KEYWORDS].

Toyoda & Crocker            Standards Track                     [Page 1]
RFC 4143                  IFAX service of ENUM             November 2005

2.  IFax Service Registration

   Service Name : "E2U+ifax"

   Type: "ifax"

   Subtype: "mailto"

   URI Scheme: "mailto"
   The URI Scheme is "mailto" because facsimile is a profile of standard
   Internet mail and uses standard Internet mail addressing.

   Functional Specification: See section 1

   Security Considerations: See section 3

   Intended usage: COMMON

   Author: Kiyoshi Toyoda (toyoda.kiyoshi@jp.panasonic.com)
           Dave Crocker (dcrocker@bbiw.net)

3.  Security Considerations

   DNS, as used by ENUM, is a globally distributed database.  Thus, any
   information stored in it is visible to anyone anonymously.  Although
   this is not qualitatively different from publication in a telephone
   directory, it does expose the data subject to automatic data
   collection without any indication that this has been done or by whom.

   Data harvesting by third parties is often used to generate lists of
   targets for unrequested information; in short, the lists are used to
   address "spam".  The publication of a telephone number in ENUM,
   especially when it is an associated Internet fax service, may be used
   to send "junk faxes", for example.

   In the case of electronic mail, users subscribed to mailing lists can
   have "sacrificial" email accounts.  These special-purpose addresses
   help the user filter out unrequested email.  This is not so easy with
   published telephone numbers.  The PSTN E.164 number assignment
   process is much more involved and less flexible; usually a single
   E.164 number (or a fixed range of numbers) is associated with each
   PSTN access.  Thus, it is not possible to use a "sacrificial" phone

   Due to the implications of publishing data in a globally accessible
   database, as a principle, the data subject MUST give explicit
   informed consent to data being published in ENUM.

Toyoda & Crocker            Standards Track                     [Page 2]
RFC 4143                  IFAX service of ENUM             November 2005

   Internet Fax is based on existing use of Internet mail.  Developers
   and users should also consider the Security Consideration sections in
   [RFC3965] and [RFC2532].

   In addition to the specific security considerations given above, the
   Security Considerations section of [ENUMbis] applies to this

4.  Example

   The following is an example of the use of IFax service in a NAPTR

        IN NAPTR 10 10 "u" "E2U+ifax:mailto"

5.  IANA Considerations

   This specification creates a DNS NAPTR registration, according to the
   terms specified in [ENUMbis].

   The registration details are contained in section 2, Fax Service

6.  References

6.1.  Normative References
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