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+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
+
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+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.
+
+
+
+
+
+
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+
+
+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
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+Wing                        Standards Track                     [Page 4]
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+RFC 2530            Media Features using DSN and MDN          March 1999
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+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.
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+Wing                        Standards Track                     [Page 5]
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