Simplified POP/IMAP Downgrading for Internationalized Email

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Last updated 2012-08-13
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Network Working Group                                   Arnt Gulbrandsen
Internet-Draft                                               August 2012
Intended Status: Proposed Standard
Updates: 3501

      Simplified POP/IMAP Downgrading for Internationalized Email

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Gulbrandsen               Expires January 2013                  [Page 1]
Internet-draft                                               August 2012


   This document specifies a method for IMAP and POP servers to serve
   internationalized messages to conventional clients. The specification
   is simple, easy to implement and provides only rudimentary results.

1. Overview

   It may happen that a conventional IMAP or POP client opens a mailbox
   containing internationalized messages, or even attempt to read
   internationalized messages, for instance when a user has both
   internationalized and conventional MUAs.

   Some operations cannot be performed by conventional clients. Most
   importantly, an internationalized message usually contains at least
   one internationalized address, so address-based operations are only
   rarely possible. This includes displaying the addresses, replying,
   and most types of address-based signature or security processing.

   Still, the sender's name, the message subject, body text and
   attachments can easily be displayed, so a helpful IMAP/POP server may
   prefer to provide access to what it can rather than hide the message

   This document specifies a way to present such messages to the client.
   It values simplicity of implementation over fidelity of
   representation, since implementing a high-fidelity downgrade
   algorithm is likely more work than implementing proper support for
   [RFC5721] and/or [RFC5738].

   The server is assumed to be internationalized internally, and to
   store messages internationalized messages natively. When it needs to
   present an internationalized message to a conventional client, it
   synthesizes a conventional message containing most of the information
   and presents that (the "synthetic message").

2. Information preserved and lost

   The synthetic message is intended to convey the most important
   information to the user. Where information is lost, the user should
   see the message as incomplete rather than modified.

   The synthetic message is not intended to convey any information to
   the client software that would require or enable it to apply special
   handling to the message. Client authors who wish to handle
   internationalized messages are encouraged to implement [RFC5738].

Gulbrandsen               Expires January 2013                  [Page 2]
Internet-draft                                               August 2012

   Upper case in examples represents non-ASCII. is a plain
   domain, represents a non-ASCII domain in the .com top-
   level domain.

2.1 Email addresses

   Each internationalized email address in the header fields listed
   below is replaced with an invalid email address whose display-name
   tells the user what happened.

   The format of the display-name is explicitly unspecified. Anything
   which tells the user what happened is good. Anything which produces
   an email address which might belong to someone else is bad.

   Given an internationalized address "Fred Foo <>", an
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