Network Working Group                                      C. Allocchio
Request for Comments: 2304                                   GARR-Italy
Category: Standards Track                                    March 1998

              Minimal FAX address format in Internet Mail

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 (1998).  All Rights Reserved.


   This memo describes a simple method of encoding PSTN addresses of
   facsimile devices in the local-part of Internet email addresses.

   As with all Internet mail addresses, the left-hand-side (local- part)
   of an address generated according to this specification, is not to be
   interpreted except by the MTA that is named on the right-hand-side

1. Introduction

   Since the very first e-mail to fax gateway objects appeared, a number
   of different methods to specify a fax address as an e-mail address
   have been used by implementors. Two major objectives for this were

     - enable an e-mail user to send faxes from his/her e-mail

     - enable some kind of "fax over e-mail service" transport, to
       reduce the costs of fax transmissions, and use the existing
       e-mail infrastructure.

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RFC 2304               Minimal FAX address format             March 1998

   This memo describes the MINIMAL addressing method and standard
   extensions to encode FAX addresses in e-mail addresses, as required
   in reference [13]. The opposite problem, i.e. to allow a traditional
   numeric-only fax device user to access the e-mail transport service,
   is not discussed here.

   All implementations supporting this FAX over e-mail address format
   MUST support as a minimum the specification described in this
   document.  The generic complex case of converting the whole PSTN
   addressing in e-mail is out of scope in this minimal specification:
   there is some work in progress in the field, where also a number of
   standard optional extensions are being defined.

   In this document the formal definitions are described using ABNF
   syntax, as defined into [7]. We will also use some of the "CORE
   DEFINITIONS" defined in "APPENDIX A - CORE" of that document. The
   exact meaning of the capitalised words


   is defined in reference [6].

2. Minimal Fax address

   The "service-selector" defined in section 2 of reference [13] for the
   fax service is:

      service-selector = "FAX"

   The minimal addressing for the fax service also requires support for
   a "qualif-type1" element (see section 2 of reference [13]).  This
   element is an OPTIONAL element of the fax address, but its support,
   when present, is REQUIRED:

      qualif-type1 = "/" t33-sep "=" sub-addr


      t33-sep = "T33S"

      sub-addr = 1*( DIGIT )

   Thus, the minimal specification of a fax in e-mail address is:

      fax-address = fax-mbox [ "/T33S=" sub-addr ]

      fax-mbox = "FAX=" global-phone

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     See section 4.1 in case multiple sub-addr per fax-mbox need to be

   The Minimal supported syntax for global-phone (as described in
   section reference [13]) is:

   global-phone = "+" 1*( DIGIT , written-sep )

   written-sep = ( "-" / "." )

   The use of other dialling schemas for PSTN numbers (like private
   numbering plans or local dialling conventions) is also allowed.
   However, this does not preclude nor remove the minimal compulsory
   requirement to support the "global-phone" syntax as defined above.

   Any non "global-phone" dialling schema MUST NOT use the leading "+"
   between the "=" sign and the dialling string. The "+" sign is
   strictly reserved for the standard "global-phone" syntax.

     The specification of these different dialling schemas is out of
     scope for this minimal specification.

   User specification of PSTN e-mail addresses will be facilitated if
   they can insert these separators between dial elements like digits
   etc.  For this reason we allow them in the syntax the written-sep

   Implementors' note:
     Use of the written-sep elements is allowed, but not recommended.
     Any occurences of written-sep elements in a pstn-mbox MUST be
     ignored by all conformant implementations. User Agents SHOULD
     remove written-sep elements before submitting messages to the
     Message Transport System.

2.2 Some examples of a minimal "fax-address"




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3. The e-mail address of the I-fax device: mta-I-fax

   An "I-fax device" has an e-mail address, or to be more exact, a name
   which enables a mail system to identify it on the e-mail global

   In Internet mail, this is the Right Hand Side (RHS) part of the
   address, i.e. the part on the right of the "@" sign. We will call
   this mta-I-fax

      mta-I-fax = domain

   For "domain" strings used in SMTP transmissions, the string MUST
   conform to the requirements of that standard's <domain>
   specifications [1], [3].  For "domain" strings used in message
   content headers, the string MUST conform to the requirements of the
   relevant standards [2], [3].

   Note: in both cases, the standards permit use of "domain names" or
         "domain literals" in addresses.

4. The fax-email

   The complete structure used to transfer a minimal FAX address over
   the Internet e-mail transport system is called "fax-email". This
   object is an e-mail address which conforms to RFC822 [2] and RFC1123
   [3] "addr-spec" syntax, with some extra structure which allows the
   FAX number to be identified.

         fax-email =  ["/"] fax-address ["/"] "@" mta-I-fax

   Implementors' note:
     The optional "/" characters can result from other mail transport
     services gateways, where it is also an optional element.
     Implementations MUST accept the optional slashes but SHOULD NOT
     generate them. Gateways are allowed to strip them off when
     converting to Internet mail addressing.

     It is essential to remind that "fax-address" element MUST strictly
     follow the "quoting rules" spcified in the relevant standards [2],

4.1 Multiple subaddresses

   In case a particular service requires multiple T.33 subaddresses, and
   these subaddresses need to be given on the same "fax-mbox", multiple
   "fax-email" elements will be used.

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   Implementors' note:
     The UA could accept multiple subaddress elements for the same
     global-phone, but it must generate multiple "fax-mbox" elements
     when passing the message to the MTA.

4.2 Some examples of minimal "fax-email"



5. Conclusion

   This proposal creates a minimal standard encoding for FAX addresses
   within the global e-mail transport system. The proposal requires no
   changes to existing e-mail software.

6. Security Considerations

   This document specifies a means by which FAX addresses can be encoded
   into e-mail addresses. As routing of e-mail messages is determined by
   Domain Name System (DNS) information, a successful attack on this
   service could force the mail path via some particular gateway or
   message transfer agent where mail security can be affected by
   compromised software.

   There are several means by which an attacker might be able to deliver
   incorrect mail routing information to a client. These include: (a)
   compromise of a DNS server, (b) generating a counterfeit response to
   a client's DNS query, (c) returning incorrect "additional
   information" in response to an unrelated query. Clients SHOULD ensure
   that mail routing is based only on authoritative answers. Once DNS
   Security mechanisms [5] become more widely deployed, clients SHOULD
   employ those mechanisms to verify the authenticity and integrity of
   mail routing records.

   7. Author's Address

   Claudio Allocchio
   Sincrotrone Trieste
   SS 14 Km 163.5 Basovizza
   I 34012 Trieste

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   X.400:  C=it;A=garr;P=Trieste;O=Elettra;
   Phone:  +39 40 3758523
   Fax:    +39 40 3758565

8. References

   [1]  Postel, J., "Simple Mail Transfer Protocol", STD 10, RFC 821,
        August 1982.

   [2]  Crocker, D., " Standard for the format of ARPA Internet text
        messages", STD 11, RFC 822, August 1982.

   [3]  Braden, R., "Requirements for Internet hosts - application and
        support", RFC 1123, October 1989.

   [4]  Malamud, C. and M. Rose, "Principles of Operation for the
        TPC.INT Subdomain: Remote Printing -- Technical Procedures", RFC
        1528, October 1993.

   [5]  Eastlake, D. and C. Kaufman, "Domain Name System Security
        Extensions", RFC 2065, January 1997.

   [6]  Bradner, S., "Key words for use in RFCs to Indicate Requirement
        Levels", RFC 2119, March 1997.

   [7]  Crocker, D. and P. Overell, "Augmented BNF for Syntax
        Specifications", RFC 2234, November 1997.

   [8]  ITU F.401 - Message Handling Services: Naming and Addressing for
        Public Message Handling Service; recommendation F.401 (August

   [9]  ITU F.423 - Message Handling Services: Intercommunication
        Between the Interpersonal Messaging Service and the Telefax
        Service; recommendation F.423 (August 1992)

   [10] ITU E.164 - Numbering plan for the ISDN era; recommendation
        E.164/I.331 (August 1991)

   [11] ITU T.33 - Facsimile routing utilizing the subaddress;
        recommendation T.33 (July, 1996)

   [12] ETSI I-ETS 300,380 - Universal Personal Telecommunication
        (UPT): Access Devices Dual Tone Multi Frequency (DTMF) sender
        for acoustical coupling to the microphone of a handset telephone
        (March 1995)

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   [13] Allocchio, C., " Minimal FAX address format in Internet Mail",
        RFC 2303, March 1998.

   [14] Kille, S., "MIXER (Mime Internet X.400 Enhanced Relay): Mapping
        between X.400 and RFC 822/MIME", RFC 2156, January 1998.

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9.  Full Copyright Statement

   Copyright (C) The Internet Society (1998).  All Rights Reserved.

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph are
   included on all such copies and derivative works.  However, this
   document itself may not be modified in any way, such as by removing
   the copyright notice or references to the Internet Society or other
   Internet organizations, except as needed for the purpose of
   developing Internet standards in which case the procedures for
   copyrights defined in the Internet Standards process must be
   followed, or as required to translate it into languages other than

   The limited permissions granted above are perpetual and will not be
   revoked by the Internet Society or its successors or assigns.

   This document and the information contained herein is provided on an

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