RFC2304 - Minimal FAX address format in Internet Mail

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.

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.

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 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

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

Note:

See section 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=+33-1-88335215

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

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 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],

[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.

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.org

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

Italy

RFC822: 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 3758565

8. References

[1] Postel, J., "Simple Mail Transfer Protocol", STD 10, RFC821,

August 1982.

[2] Crocker, D., " Standard for the format of ARPA Internet text

messages", STD 11, RFC822, August 1982.

[3] Braden, R., "Requirements for Internet hosts - application and

support", RFC1123, 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", RFC2065, January 1997.

[6] Bradner, S., "Key words for use in RFCs to Indicate Requirement

Levels", RFC2119, March 1997.

[7] Crocker, D. and P. Overell, "Augmented BNF for Syntax

Specifications", RFC2234, 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)

[13] Allocchio, C., " Minimal FAX address format in Internet Mail",

RFC2303, March 1998.

[14] Kille, S., "MIXER (Mime Internet X.400 Enhanced Relay): Mapping

between X.400 and RFC822/MIME", RFC2156, January 1998.

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