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. 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. 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].
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]. RFC1893]. This status code may be returned
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"). [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.