RFC 2304

RFC 2304: Minimal FAX address format in Internet Mail 📠✨

Okay bestie, this RFC is all about squishing a fax number into an email address, and it's giving very organised main character energy 💅🦋. Here's the title block tea:

• RFC number: 2304 🌸
• Title: Minimal FAX address format in Internet Mail
• Author: C. Allocchio (Claudio Allocchio), GARR-Italy 💖
• Category: Standards Track 🎀
• Date: March 1998 🗓️
• Obsoletes / Updates: the title block doesn't list either one ✨

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Status of this Memo 📜

This document specifies an Internet standards track protocol for the Internet community, and it's asking for discussion and suggestions for improvements 🫶. For the standardisation state and status of this protocol, check the current edition of the "Internet Official Protocol Standards" (STD 1). Distribution of this memo is unlimited 🌈.

Copyright Notice ©️

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

IESG NOTE 🧚

This memo describes a simple way to encode PSTN addresses of fax devices in the local-part of Internet email addresses 📠💌.

Like every Internet mail address, the left-hand side (local-part) of an address made under this spec is not to be interpreted by anyone except the MTA named on the right-hand side (domain). That's the rule, no cap 🙈.

1. Introduction 🌷

Ever since the very first email-to-fax gateway objects showed up, implementors have been inventing their own ways to write a fax address as an email address 🍓. Two big goals kept coming up:

• letting an email user send faxes straight from their email interface 💌
• enabling some kind of "fax over email service" transport, so faxes can ride the existing email infrastructure and cost less 💸

This memo describes the minimal addressing method, plus standard extensions, for encoding FAX addresses in email addresses, as required in reference [13]. The opposite problem, letting a traditional number-only fax device user reach the email transport service, is not covered here 🙅‍♀️.

All implementations supporting this FAX-over-email address format MUST support, as a minimum, the specification in this document 👑. Converting the whole PSTN addressing scheme into email is out of scope for this minimal spec. There's some work in progress on that front, along with a number of standard optional extensions being defined 🚧.

Formal definitions here use ABNF syntax, as defined in [7]. We also borrow some of the "CORE DEFINITIONS" from "APPENDIX A - CORE" of that document. The exact meaning of the capitalised words below is defined in reference [6]:

"MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD",
"SHOULD NOT", "RECOMMENDED",  "MAY", "OPTIONAL"

2. Minimal Fax address 💖

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

service-selector = "FAX"

Minimal addressing for the fax service also needs support for a "qualif-type1" element (see section 2 of reference [13]). This element is OPTIONAL in a fax address, but when it's present, its support is REQUIRED 🎀:

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

where

t33-sep = "T33S"

sub-addr = 1*( DIGIT )

So the minimal spec for a fax in an email address looks like this ✨:

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

fax-mbox = "FAX=" global-phone

Note: check section 4.1 if you need multiple sub-addr per fax-mbox 👀.

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

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

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

Other dialling schemes for PSTN numbers, like private numbering plans or local dialling conventions, are also allowed 🌍. That doesn't cancel or remove the minimal compulsory requirement to support the "global-phone" syntax above.

Any non "global-phone" dialling scheme MUST NOT use the leading "+" between the "=" sign and the dialling string 🚫. The "+" sign is strictly reserved for the standard "global-phone" syntax, full stop 💅.

Note: the specs for those different dialling schemes are out of scope for this minimal spec 🙃.

Users will have an easier time writing PSTN email addresses if they can put separators between dial elements, like digits 🔢. So the written-sep element lets them use those separators in the syntax 🫧.

Implementors' note: using written-sep elements is allowed, but not recommended 🙈. Any occurrences of written-sep elements in a pstn-mbox MUST be ignored by all conformant implementations. User Agents SHOULD remove written-sep elements before they submit 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. To be more exact, it has a name that lets a mail system identify it on the global e-mail system 🌐.

In Internet mail, that name is the Right Hand Side (RHS) of the address, meaning the part to the right of the "@" sign. This memo calls it 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 let you use "domain names" or "domain literals" in addresses 🌸.

4. The fax-email 💅

The complete structure used to carry a minimal FAX address over the Internet e-mail transport system is called "fax-email" ✨. This object is an e-mail address that follows the RFC822 [2] and RFC1123 [3] "addr-spec" syntax, with some extra structure so the FAX number can be identified 📠.

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

Implementors' note: the optional "/" characters can come from other mail transport service gateways, where they're also optional 🦋. 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's essential to remember that the "fax-address" element MUST strictly follow the "quoting rules" specified in the relevant standards [2], [3] 🔥.

4.1 Multiple subaddresses 👯

Sometimes a particular service needs multiple T.33 subaddresses, and they need to go on the same "fax-mbox". For that, multiple "fax-email" elements are 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

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9. Full Copyright Statement ✨

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

okay so the legal part is here, and it's actually pretty chill 🫶 You can copy this document and pass it along to your besties, and you can make derivative works that comment on it, explain it, or help people implement it. Those can be published, copied, and distributed, in whole or in part, with no restrictions of any kind, as long as the copyright notice and this paragraph are included on every copy and derivative work. ✨

The document itself is a different story 🙅‍♀️ It may not be modified in any way, so you can't remove the copyright notice or the references to the Internet Society or other Internet organizations. The exceptions are if you're developing Internet standards (then you have to follow the copyright procedures in the Internet Standards process 📜) or if you're translating it into languages other than English 🌍

The limited permissions above are perpetual and won't be revoked by the Internet Society or its successors or assigns. Forever and ever 🧚💜

And now the disclaimer, which is giving serious energy 💀

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.

Basically, nobody is promising that using this stuff won't infringe anyone's rights, and there are no implied warranties of merchantability or fitness for a particular purpose 😭 Read it with your eyes open, bestie 👀✨