RFC 2530

RFC 2530: Indicating Supported Media Features Using Extensions to DSN and MDN 💖

okay bestie, this is an Internet standards track doc from March 1999 🎀 Here's the title block:

• Network Working Group, RFC number 2530
• Author: D. Wing (Dan Wing) of Cisco Systems 🧚
• Category: Standards Track
• Date: March 1999
• Obsoletes / Updates: nothing is listed in the title block, so this one doesn't obsolete or update anything 🦋

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Status of This Memo

this doc specifies an Internet standards track protocol for the Internet community, and it's asking for discussion and suggestions for improvements 🫶 For the standardization 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 (1999). All Rights Reserved. 💅

1. Abstract ✨

so there's a need in Internet mail and Internet fax for a recipient to say which media features it supports. that way senders can make messages without going over what the recipient can actually handle 🌸

this memo describes a format for generating Message Disposition Notifications [RFC2298] and Delivery Status Notifications [RFC1894] that carry that info. senders can use it to avoid going over the recipient's capabilities when they send later messages. it's giving smart 🧠

2. Introduction

the extensions in this doc can go in Message Disposition Notifications [RFC2298] or Delivery Status Notifications [RFC1894], whichever fits the implementation 💜

quick heads up that both DSNs and MDNs have drawbacks 🙈 DSNs aren't available between all senders and receivers, and MDNs make the receiver disclose message disposition information. (If they use the "denied" disposition-type, that also means disclosing the time the disposition notification was generated.)

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. 🎀

3. Extensions for use by DSN and MDN 🍓

the following extension works for both DSN [RFC1894] and MDN [RFC2298] messages ✨

for a DSN message, the per-recipient fields below are defined (section 2.3 of [RFC1894]). for an MDN message, the extension fields below are defined (section 3.1 of [RFC2298]). the grammar uses the language of [RFC2234]:

extension-field    = media-features CRLF

media-features     = "Media-Accept-Features" ":"
                      media-feature-tags
media-feature-tags = <*text as defined below,
                      with LWSP wrapping>

the <media-feature-tags> are defined in separate schema documents, which MUST utilize the language described in [SYNTAX]. the schema MUST be registered following the registration requirements of [RFC2506]. 👑

3.1. Examples 🧚‍♀️

these examples assume there's a schema document that defines the tags shown 💅

3.1.1. Paper-size and Color

assuming there's a schema document that describes the tags paper-size and color, this one is valid:

Media-Accept-Features: (& (paper-size=a4) (color=binary) )

3.1.2. UA-Media, Paper-size, and Color

assuming there's a schema document that describes the tags paper-size, color, and grey:

Media-Accept-Features: (& (| (paper-size=a4) (paper-size=letter) )
  (| (& (color=grey) (dpi=200) (dpi-xyratio=200/100) )
  (& (color=limited) (dpi=200) (dpi-xy=200/100) ) )

4. MTA Implmentation Recommendation 🦋

okay so if the recipient's MTA figures out a message can't be processed, the MTA is strongly encouraged to reject it with status code 5.6.1 [RFC1893] 🫶 That status code can come back in response to the end-of-mail-data indicator if the MTA supports enhanced error codes [RFC2034]. Or it can come after the message is received, by generating a delivery failure DSN ("bounce").

5. Security Considerations 🔥

⚠️ this part is serious, so read it carefully bestie 💀

inaccurate media feature info could cause a denial of service. senders would keep sending messages the recipient can't process 😭

the media feature info could also be inaccurate because of a malicious attack (a spoofed DSN or MDN) or because of misconfiguration 🙈

6. Acknowledgments 🫶

the author thanks the members of the Internet Fax working group for helping with this doc, especially Larry Masinter, Graham Klyne, and Ned Freed 💖

7. References 📚

• [RFC2506] Holtman, K., Mutz, A. and T. Hardie, "Media Feature Tag Registration Procedure", BCP 31, RFC 2506, March 1999.
• [RFC1894] Moore, K. and G. Vaudreuil, "An Extensible Message Format for Delivery Status Notifications", RFC 1894, January 1996.
• [RFC2034] Freed, N., "SMTP Service Extension for Returning Enhanced Error Codes", RFC 2034, October 1996.
• [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.
• [RFC2234] Crocker, D. and P. Overell, "Augmented BNF for Syntax Specifications: ABNF", RFC 2234, November 1997.
• [RFC2298] Fajman, R., "An Extensible Message Format for Message Disposition Notifications", RFC 2298, March 1998.
• [SYNTAX] Klyne, G., "A Syntax for Describing Media Feature Sets", RFC 2533, March 1999.

8. Author's Address 💌

Dan Wing
Cisco Systems, Inc.
101 Cooper Street
Santa Cruz, CA 95060  USA

Phone: +1 831 457 5200
Fax:   +1 831 457 5208
EMail: dwing@cisco.com

9. Full Copyright Statement 💜

legal stuff, but it's important, so here's all of it:

Copyright (C) The Internet Society (1999). 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. 🌈