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Network Working Group                                      C. AllocchioRequest for Comments: 2304                                   GARR-ItalyCategory: Standards Track                                    March 1998Minimal FAX address format in Internet MailStatus 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.IESG NOTE   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   (domain).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       interface;     - enable some kind of "fax over e-mail service" transport, to       reduce the costs of fax transmissions, and use the existing       e-mail infrastructure.Allocchio                   Standards Track                     [Page 1]

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      "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD",      "SHOULD NOT", "RECOMMENDED",  "MAY", "OPTIONAL"   is defined in reference [6].2. Minimal Fax address   The "service-selector" defined insection 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 (seesection 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   where      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-phoneAllocchio                   Standards Track                     [Page 2]

RFC 2304               Minimal FAX address format             March 1998   Note:     Seesection 4.1 in case multiple sub-addr per fax-mbox need to be     specified.   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.   Note:     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   element.   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"      FAX=+3940226338      FAX=+12027653000/T33S=1387      FAX=+33-1-88335215Allocchio                   Standards Track                     [Page 3]

RFC 2304               Minimal FAX address format             March 19983. 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   system.   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 toRFC822 [2] andRFC1123   [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],     [3]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.Allocchio                   Standards Track                     [Page 4]

RFC 2304               Minimal FAX address format             March 1998   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"      FAX=+3940226338@faxworld.org      FAX=+12027653000/T33S=1387@faxworld.org      /FAX=+33-1-88335215/@faxworld.org5. 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   ItalyAllocchio                   Standards Track                     [Page 5]

RFC 2304               Minimal FAX address format             March 1998RFC822: Claudio.Allocchio@elettra.trieste.it   X.400:  C=it;A=garr;P=Trieste;O=Elettra;           S=Allocchio;G=Claudio;   Phone:  +39 40 3758523   Fax:    +39 40 37585658. 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",RFC1528, 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        1992)   [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)Allocchio                   Standards Track                     [Page 6]

RFC 2304               Minimal FAX address format             March 1998   [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 andRFC 822/MIME",RFC 2156, January 1998.Allocchio                   Standards Track                     [Page 7]

RFC 2304               Minimal FAX address format             March 19989.  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   English.   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   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.Allocchio                   Standards Track                     [Page 8]