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rfc:rfc2530

Network Working Group D. Wing Request for Comments: 2530 Cisco Systems Category: Standards Track March 1999

             Indicating Supported Media Features Using
                     Extensions to DSN and MDN

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.

Copyright Notice

 Copyright (C) The Internet Society (1999).  All Rights Reserved.

1. Abstract

 There is a need in Internet mail and Internet fax for a recipient to
 indicate the media features it supports so that messages can be
 generated by senders without exceeding the recipient's abilities.
 This memo describes a format for generating Message Disposition
 Notifications [RFC2298] and Delivery Status Notifications [RFC1894]
 which contain such information.  This information can be used by
 senders to avoid exceeding the recipient's capabilities when sending
 subsequent messages.

2. Introduction

 The extensions described in this document can be used in Message
 Disposition Notifications [RFC2298] or Delivery Status Notifications
 [RFC1894], as appropriate for the implementation.
 Note that both DSNs and MDNs have drawbacks: DSNs are not available
 between all senders and receivers, and MDNs require the receiver to
 disclose message disposition information (or, if using the "denied"
 disposition-type, 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].

Wing Standards Track [Page 1] RFC 2530 Media Features using DSN and MDN March 1999

3. Extensions for use by DSN and MDN

 The following extension is available to both DSN [RFC1894] and MDN
 [RFC2298] messages.
 For a DSN message, the following per-recipient fields are defined
 (section 2.3 of [RFC1894]).  For an MDN message, the following
 extension fields are defined (section 3.1 of [RFC2298]).  Using 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

 The following examples assume there is a schema document which
 defines the tags shown.

3.1.1. Paper-size and Color

 Assuming there is a schema document which describes the tags paper-
 size and color, the following example is valid:
    Media-Accept-Features: (& (paper-size=a4) (color=binary) )

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

 Assuming there is a schema document which 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

 If the recipient's MTA determines that a message cannot be processed,
 the recipient's MTA is strongly encouraged to reject the message with
 a status code of 5.6.1 [RFC1893].  This status code may be returned

Wing Standards Track [Page 2] RFC 2530 Media Features using DSN and MDN March 1999

 in response to the end-of-mail-data indicator if the MTA supports
 reporting of enhanced error codes [RFC2034], or after message
 reception by generating a delivery failure DSN ("bounce").

5. Security Considerations

 Inaccurate media feature information could cause a denial of service,
 causing subsequent messages to be sent which the recipient is unable
 to process.
 The media feature information could be inaccurate due to a malicious
 attack (spoofed DSN or MDN) or misconfiguration.

6. Acknowledgments

 The author thanks the members of the Internet Fax working group for
 assistance with this document, and 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.

Wing Standards Track [Page 3] RFC 2530 Media Features using DSN and MDN 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

Wing Standards Track [Page 4] RFC 2530 Media Features using DSN and MDN March 1999

9. Full Copyright Statement

 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.

Wing Standards Track [Page 5]

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