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Network Working Group                                       C. AllocchioRequest for Comments: 3192                                    GARR-ItalyObsoletes:2304                                             October 2001Updates:2846Category: Standards TrackMinimal 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 (2001).  All Rights Reserved.Abstract   This memo describes a simple method of encoding Global Switched   Telephone Network (GSTN) addresses of facsimile devices in the   local-part of Internet email addresses.1. Introduction   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).   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.  Several objectives for this methods   have been identified, like to enable an e-mail user to send and   receive faxes from his/her e-mail interface, to allow some kind of   "fax over e-mail service" transport (possibly reducing the costs of   GSTN long distance transmissions) while using the existing e-mail   infrastructure.   This memo describes the MINIMAL addressing method and standard   extensions to encode FAX addresses into 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.Allocchio                   Standards Track                     [Page 1]

RFC 3192      Minimal FAX address format in Internet Mail   October 2001   These IANA forms used to register the standard elements defined here   are given in the "IANA Considerations" chapter (section 7 of this   document).   All implementations supporting FAX over e-mail address format MUST   support this minimal specification.1.1 Terminology and Syntax conventions   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 capitalized words      "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD",      "SHOULD NOT", "RECOMMENDED", "MAY", "OPTIONAL"   is defined in reference [6].   In this document the following new terms are also defined:      I-fax device:         an I-pstn device type [13] which is able to communicate either         directly or indirectly with the traditional FAX over GSTN         service;      mta-I-fax:         the Internet domain name which identifies uniquely an I-fax         device over the Internet (see also mta-I-pstn in [13]);      fax-email:         the complete Internet e-mail address structure which is used to         transport a FAX address over the Internet e-mail service (see         also pstn-email in [13]).2. Minimal Fax address   The minimal fax address within e-mail has been defined for   consistency with reference [13] and it contains two elements: the   fax-mbox and an optional qualif-type1 element.   More precisely the GSTN minimal address specification requires the   use of a unique service-selector for each specific application   (section 2 in [13]).   The "service-selector" defined for the fax service is as follows:      service-selector = "FAX"Allocchio                   Standards Track                     [Page 2]

RFC 3192      Minimal FAX address format in Internet Mail   October 2001   In the syntax for the fax address a qualif-type1 element has been   defined for support of T.30/T.33 subaddresses (see section 2 of   [13]).  The use of this element is OPTIONAL, but compliant   implementations MUST be able to support and correctly interpret it   when present.  Its definition is as follows:      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-phone   Notes:      For the case of a single subaddress, only numbers are allowed in      <sub-addr> which is consistent with T.30, T.33, and this document.      While T.30 and T.33 use SPACE to pad its field, padding isn't      necessary in the <sub-addr> field defined by this document.      For the case of multiple subaddresses, T.33 specifies the "#"      character be used to specify multiple subaddreses.  However, only      digits are permitted in the <sub-addr> field defined by this      document.  Refer tosection 4.1 in case multiple <sub-addr> per      per <fax-mbox> need to be specified.   The Minimal supported syntax for global-phone (as described insection 2.1 of reference [13]) is:   global-phone = "+" 1*( DIGIT / written-sep )   written-sep = ( "-" / "." )   Refer to section 2.1 in [13] for other important considerations about   the global-phone element.2.2 Some examples of a minimal "fax-address"   Some examples of minimal fax-address follows:Allocchio                   Standards Track                     [Page 3]

RFC 3192      Minimal FAX address format in Internet Mail   October 2001      FAX=+3940226338      FAX=+12027653000/T33S=1387      FAX=+33-1-88335215   Note:      the examples shown are just for illustration purposes.3. The e-mail address of the I-fax device: mta-I-fax   An "I-fax device" has, among its characteristics, a unique Internet   domain name which identifies it on the Internet.  Within Internet   mail, this is the Right Hand Side (RHS) part of the address, i.e.,   the part on the right of the "@" sign.  For purposes of this document   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 standards <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:      the use of "domain names" or "domain literals" is permitted in      addresses in both the SMTP envelope and message header fields.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 a an e-mail address which conforms to [2] and [3]   "addr-spec" syntax, with structure refinements which allows the FAX   number to be identified.   fax-email = ["""] ["/"] fax-address ["/"] ["""] "@" mta-I-fax   Implementors' note:      The optional "/" characters can result from translations from      other transport gateways (such as some X.400 gateways) which have      included the "/" as an optional element.  Implementations MUST      accept the optional slashes but SHOULD NOT generate them.      Gateways are allowed to strip them off when converting to InternetAllocchio                   Standards Track                     [Page 4]

RFC 3192      Minimal FAX address format in Internet Mail   October 2001      mail addressing.  The relevant standard [2], [3] define exactly      when the optional "quotes" characters surrounding the entire local      part (i.e., the part on the left of the "@" character into the      fax-email) MUST be added.4.1 Multiple subaddresses   There are some instances in GSTN applications where multiple   subaddresses are used: T.33 subaddresses in fax service are one of   these cases.  In e-mail practice a separate and unique e-mail address   is always used for each recipient; as such, if multiple T.33   subaddresses are present, the use of multiple "fax-email" elements is   REQUIRED.   Implementors' note:      The UA MAY accept multiple subaddress elements for the same      global-phone, but it MUST generate multiple "fax-mbox" elements      when submitting the message to the MTA.4.2 Some examples of minimal "fax-email"      Some examples of minimal fax-email addresses follows:      FAX=+3940226338@faxworld.org      FAX=+12027653000/T33S=1387@faxworld.org      /FAX=+33-1-88335215/@faxworld.org   Note:      the examples shown are just for illustration purposes.5. Conclusion   This proposal creates a minimal standard encoding for FAX addresses   within the global e-mail transport system.  The proposal is   consistent with existing e-mail standards.6. Security Considerations   This document specifies a means by which FAX addresses can be encoded   into e-mail addresses.  Since e-mail routing is determined by Domain   Name System (DNS) data, a successful attack to DNS could disseminate   tampered information, which causes e-mail messages to be diverted via   some MTA or Gateway where the security of the software has been   compromised.Allocchio                   Standards Track                     [Page 5]

RFC 3192      Minimal FAX address format in Internet Mail   October 2001   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. IANA Considerations   The IANA registration forms for "FAX" service-selector and "T33S"   qualif-type1 elements are defined here.  These forms update the   previous registration forms defined in [15].7.1 IANA Registration form for updated value of GSTN    address service-selector "FAX"   To: IANA@iana.org   Subject: Registration of updated values for the GSTN address   service-selector specifier "FAX"   service-selector name:      FAX   Description of Use:      FAX - specify that the GSTN address refers either to an      Internet Fax device, or an onramp/offramp Fax gateway.      For a complete description refer toRFC 3192 andRFC 3191.   Security Considerations:      See the Security Consideration section ofRFC 3192.   Person & email address to contact for further information:   Claudio Allocchio   INFN-GARR   c/o Sincrotrone Trieste   SS 14 Km 163.5 Basovizza   I 34012 Trieste   ItalyAllocchio                   Standards Track                     [Page 6]

RFC 3192      Minimal FAX address format in Internet Mail   October 2001RFC2822: Claudio.Allocchio@garr.it   X.400:   C=it;A=garr;P=garr;S=Allocchio;G=Claudio;   Phone:   +39 040 3758523   Fax:     +39 040 37585657.2 IANA Registration form for updated value of GSTN    address qualit-type1 keyword "T33S" and value   To: IANA@iana.org   Subject: Registration of updated values for the GSTN address   qualif-type1 element "T33S"   qualif-type1 "keyword" name:      T33S   qualif-type1 "value" ABNF definition:      sub-addr = 1*( DIGIT )   Description of Use:      T33S is used to specify the numeric only optional fax sub-address      element described in "ITU T.33 - Facsimile routing utilizing the      subaddress; recommendation T.33 (July, 1996)".  Further detailed      description is available inRFC 3192.   Use Restriction:      The use of "T33S" is restricted to "FAX" service-selector, is it      has no meaning outside the fax service.   Security Considerations:      See the Security Consideration section ofRFC 3192.   Person & email address to contact for further information:      Claudio Allocchio      INFN-GARR      c/o Sincrotrone Trieste      SS 14 Km 163.5 Basovizza      I 34012 Trieste      ItalyAllocchio                   Standards Track                     [Page 7]

RFC 3192      Minimal FAX address format in Internet Mail   October 2001RFC2822: Claudio.Allocchio@garr.it      X.400:   C=it;A=garr;P=garr;S=Allocchio;G=Claudio;      Phone:   +39 040 3758523      Fax:     +39 040 37585658. Changes sinceRFC 2304 specification   Although there are no major or technical changes fromRFC 2304   specification, this section briefly describes where updates and   clarifications were introduced:   -  considering the case that telephony systems do not conform any      more to the "single/few" Public Operator paradigm, the old      definition "PSTN - Public Switched Telephone Network" was changed      into the more adequate "GSTN - Global Switched Telephone Network"      one.  However, in order to remain consistent with the previous      specification, the ABNF variables names were not changed.   -section 7 "IANA Considerations" and the IANA registration forms      for the "FAX" "service-selector" and for the "T33S" "qualif-type1"      elements were added;   -  an explicit list of "new terms" with explanations was added tosection 1.1;   -  the case when multiple T.33 subaddresses are present was described      more explicitly in order to clarify how to handle them (section4.1);   -  insection 3 the language describing "mta-I-fax" was updated to      better describe its relationship with an Internet Mail address;   -  insection 4., the quoting rules of the "fax-address" and their      practical use was made explicit both in the definition of "fax-      email" and in the Implementors' note;   -  the Author's Address was updated;   -  the References list was updates to substitute ITU E.164 (1991)      with ITU E.164 (1997).Allocchio                   Standards Track                     [Page 8]

RFC 3192      Minimal FAX address format in Internet Mail   October 20019. Author's Address   Claudio Allocchio   INFN-GARR   c/o Sincrotrone Trieste   SS 14 Km 163.5 Basovizza   I 34012 Trieste   ItalyRFC2822: Claudio.Allocchio@garr.it   X.400:   C=it;A=garr;P=garr;S=Allocchio;G=Claudio;   Phone:   +39 040 3758523   Fax:     +39 040 375856510. 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", STD 3,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",BCP 14,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 - The International Public Telecommunication Numbering        Plan E.164/I.331 (May 1997).Allocchio                   Standards Track                     [Page 9]

RFC 3192      Minimal FAX address format in Internet Mail   October 2001   [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).   [13] Allocchio, C., "Minimal GSTN address format in Internet Mail",RFC 3191, October 2001.   [14] Kille, S., "MIXER (Mime Internet X.400 Enhanced Relay): Mapping        between X.400 andRFC 822/MIME",RFC 2156, January 1998.   [15] Allocchio, C., "GSTN address element extensions in e-mail        services",RFC 2846, June 2000.Allocchio                   Standards Track                    [Page 10]

RFC 3192      Minimal FAX address format in Internet Mail   October 2001Full Copyright Statement   Copyright (C) The Internet Society (2001).  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.Acknowledgement   Funding for the RFC Editor function is currently provided by the   Internet Society.Allocchio                   Standards Track                    [Page 11]