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 (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].
2. IFax Service Registration
Service Name : "E2U+ifax"
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 (firstname.lastname@example.org)
Dave Crocker (email@example.com)
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.
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
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
6.1. Normative References
[KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[ENUMbis] Faltstrom, P. and M. Mealling, "The E.164 to Uniform
Resource Identifiers (URI) Dynamic Delegation Discovery
System (DDDS) Application (ENUM)", RFC 3761, April 2004.
[RFC3965] Toyoda, K., Ohno, H., Murai, J., and D. Wing, "A Simple
Mode of Facsimile Using Internet Mail", RFC 3965, December
[RFC2532] Masinter, L. and D. Wing, " Extended Facsimile Using
Internet Mail", RFC 2532, March 1999.
[FFPIM] Crocker, D. and G. Klyne, "Full-mode Fax Profile for
Internet Mail (FFPIM)", RFC 4142, November 2005.
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