Network Working Group P. Resnick Internet-Draft Qualcomm Incorporated Updates: 3501 (if approved) C. Newman Intended status: Experimental Sun Microsystems Expires: March 9, 2010 September 5, 2009 IMAP Support for UTF-8 draft-ietf-eai-imap-utf8-08 Status of this Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and BCP 79. This document may contain material from IETF Documents or IETF Contributions published or made publicly available before November 10, 2008. The person(s) controlling the copyright in some of this material may not have granted the IETF Trust the right to allow modifications of such material outside the IETF Standards Process. Without obtaining an adequate license from the person(s) controlling the copyright in such materials, this document may not be modified outside the IETF Standards Process, and derivative works of it may not be created outside the IETF Standards Process, except to format it for publication as an RFC or to translate it into languages other than English. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on March 9, 2010. Copyright Notice Copyright (c) 2009 IETF Trust and the persons identified as the document authors. All rights reserved. Resnick & Newman Expires March 9, 2010 [Page 1] Internet-Draft IMAP Support for UTF-8 September 2009 This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents in effect on the date of publication of this document (http://trustee.ietf.org/license-info). Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Abstract This specification extends the Internet Message Access Protocol version 4rev1 (IMAP4rev1) to support unencoded international characters in user names, mail addresses and message headers. Table of Contents 1. Conventions Used in this Document . . . . . . . . . . . . . . 3 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. UTF8 IMAP Capability . . . . . . . . . . . . . . . . . . . . . 3 3.1. IMAP UTF-8 Quoted Strings . . . . . . . . . . . . . . . . 3 3.2. UTF8 Parameter to SELECT and EXAMINE . . . . . . . . . . . 5 3.3. UTF-8 LIST and LSUB Responses . . . . . . . . . . . . . . 5 3.4. UTF-8 Interaction with IMAP4 LIST Command Extensions . . . 6 3.4.1. UTF8 and UTF8ONLY LIST Selection Options . . . . . . . 6 3.4.2. UTF8 LIST Return Option . . . . . . . . . . . . . . . 6 4. UTF8=APPEND Capability . . . . . . . . . . . . . . . . . . . . 7 5. UTF8=USER Capability . . . . . . . . . . . . . . . . . . . . . 7 6. UTF8=ALL Capability . . . . . . . . . . . . . . . . . . . . . 7 7. UTF8=ONLY Capability . . . . . . . . . . . . . . . . . . . . . 7 8. Up-Conversion Server Requirements . . . . . . . . . . . . . . 8 9. Issues with UTF-8 Header Mailstore . . . . . . . . . . . . . . 9 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 11. Security Considerations . . . . . . . . . . . . . . . . . . . 11 12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11 12.1. Normative References . . . . . . . . . . . . . . . . . . . 11 12.2. Informative References . . . . . . . . . . . . . . . . . . 12 Appendix A. Design Rationale . . . . . . . . . . . . . . . . . . 13 Appendix B. Acknowledgments . . . . . . . . . . . . . . . . . . . 14 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14 Resnick & Newman Expires March 9, 2010 [Page 2] Internet-Draft IMAP Support for UTF-8 September 2009 1. Conventions Used in this Document The key words "MUST", "MUST NOT", "SHOULD", "SHOULD NOT", and "MAY" in this document are to be interpreted as defined in "Key words for use in RFCs to Indicate Requirement Levels" [RFC2119]. The formal syntax use the Augmented Backus-Naur Form (ABNF) [RFC5234] notation including the core rules defined in Appendix B of RFC 4234. In addition, rules from IMAP4rev1 [RFC3501], UTF-8 [RFC3629], Collected extensions to IMAP4 ABNF [RFC4466], and IMAP4 LIST Command Extensions [RFC5258] are also referenced. In examples, "C:" and "S:" indicate lines sent by the client and server respectively. If a single "C:" or "S:" label applies to multiple lines, then the line breaks between those lines are for editorial clarity only and are not part of the actual protocol exchange. 2. Introduction This specification extends IMAP4rev1 [RFC3501] to permit unencoded UTF-8 [RFC3629] in headers as described in Internationalized Email Headers [RFC5335]. It also adds a mechanism to support mailbox names, login names and passwords using the UTF-8 charset. This specification creates five new IMAP capabilities to allow servers to advertise these new extensions, along with two new IMAP list extensions and a new IMAP list return option. 3. UTF8 IMAP Capability The basic "UTF8" capability indicates the server supports UTF-8 quoted strings, the "UTF8" parameter to SELECT and EXAMINE, and UTF-8 responses from the LIST and LSUB commands. A client MUST use the "ENABLE UTF8" command (defined in [RFC5161]) to indicate to the server that the client accepts UTF-8 quoted-strings. The "ENABLE UTF8" command MUST only be used in the authenticated state. 3.1. IMAP UTF-8 Quoted Strings The IMAP4rev1 [RFC3501] base specification forbids the use of 8-bit characters in atoms or quoted strings. Thus a UTF-8 string can only be sent as a literal. This can be inconvenient from a coding standpoint, and unless the server offers IMAP4 non-synchronizing literals [RFC2088], this requires an extra round trip for each UTF-8 Resnick & Newman Expires March 9, 2010 [Page 3] Internet-Draft IMAP Support for UTF-8 September 2009 string sent by the client. When the IMAP server advertises the "UTF8" capability, it informs the client that it supports native UTF-8 quoted-strings with the following syntax: string =/ utf8-quoted utf8-quoted = "*" DQUOTE *UQUOTED-CHAR DQUOTE UQUOTED-CHAR = QUOTED-CHAR / UTF8-2 / UTF8-3 / UTF8-4 ; UTF8-2, UTF8-3, and UTF8-4 are as defined in RFC 3629 When this quoting mechanism is used by the client (specifically an octet sequence beginning with *" and ending with "), then the server MUST reject octet sequences with the high bit set that fail to comply with the formal syntax in [RFC3629] with a BAD response. The IMAP server MUST NOT send utf8-quoted syntax to the client unless the client has indicated support for that syntax by using the "ENABLE UTF8" command. If the server advertises the UTF8 capability, the client MAY use utf8-quoted syntax with any IMAP argument that permits a string (including astring and nstring). However, if characters outside the US-ASCII repertoire are used in an inappropriate place, the results would be the same as if other syntacticly valid but semantically invalid characters were used. For example, if the client includes UTF-8 characters in the user or password arguments (and the server has not advertised UTF8-USER), the LOGIN command will fail as it would with any other invalid user name or password. Specific cases where UTF-8 characters are permitted or not permitted are described in the following paragraphs. All IMAP servers that advertise the UTF8 capability SHOULD accept UTF-8 in mailbox names, and those that also support the "Mailbox International Naming Convention" described in RFC 3501 section 5.1.3 MUST accept utf8-quoted mailbox names and convert them to the appropriate internal format. Mailbox names MUST comply with the Net- Unicode Definition (section 2 of [RFC5198]) with the specific exception that they MUST NOT contain control characters (0000-001F, 0080-009F), delete (007F), line separator (2028) or paragraph separator (2029). An IMAP client MUST NOT issue a SEARCH command that uses a mixture of utf8-quoted syntax and a SEARCH CHARSET other than UTF-8. If an IMAP server receives such a SEARCH command, it SHOULD reject the command with a BAD response (due to the conflicting charset labels). Resnick & Newman Expires March 9, 2010 [Page 4] Internet-Draft IMAP Support for UTF-8 September 2009 3.2. UTF8 Parameter to SELECT and EXAMINE The "UTF8" capability also indicates the server supports the UTF8 parameter to SELECT and EXAMINE. When a mailbox is selected with the UTF8 parameter, it alters the behavior of all IMAP commands related to message sizes, message headers and MIME body headers so they refer to the message with UTF-8 headers. If the mailstore is not UTF-8 header native and the SELECT or EXAMINE command with UTF-8 header modifier succeeds, then the server MUST return results as if the mailstore was UTF-8 header native with upconversion requirements as described in Section 8. The server MAY reject the SELECT or EXAMINE command with the [NOT-UTF-8] response code, unless the UTF8=ALL or UTF8=ONLY capability is advertised. Servers MAY include mailboxes that can only be selected or examined if the UTF8 parameter is provided. However, such mailboxes MUST NOT be included in the output of an unextended LIST, LSUB or equivalent command. If a client attempts to SELECT or EXAMINE such mailboxes without the UTF8 parameter, the server MUST reject the command with a [UTF-8-ONLY] response code. As a result, such mailboxes will not accessible by IMAP clients written prior to this specification and are discouraged unless the server advertises UTF8=ONLY or the server implements IMAP4 LIST Command Extensions [RFC5258]. utf8-select-param = "UTF8" ;; Conforms to from RFC 4466 C: a SELECT newmailbox (UTF8) S: ... S: a OK SELECT completed C: b FETCH 1 (SIZE ENVELOPE BODY) S: ... < UTF-8 header native results > S: b OK FETCH completed C: c EXAMINE legacymailbox (UTF8) S: c NO [NOT-UTF-8] Mailbox does not support UTF-8 access C: d SELECT funky-new-mailbox S: d NO [UTF-8-ONLY] Mailbox requires UTF-8 client 3.3. UTF-8 LIST and LSUB Responses After an IMAP client successfully issues an "ENABLE UTF8" command, the server MUST NOT return in LIST results any mailbox names to the client following the IMAP4 Mailbox International Naming Convention. Instead, the server MUST return any mailbox names with characters outside the US-ASCII repertoire using utf8-quoted syntax. (The IMAP4 Resnick & Newman Expires March 9, 2010 [Page 5] Internet-Draft IMAP Support for UTF-8 September 2009 Mailbox International Naming Convention has proved problematic in the past, so the desire is to make this syntax obsolete as quickly as possible.) 3.4. UTF-8 Interaction with IMAP4 LIST Command Extensions When an IMAP server advertises both the "UTF8" capability and the "LIST-EXTENEDED" [RFC5258] capability, the server MUST support the LIST extensions described in this section. 3.4.1. UTF8 and UTF8ONLY LIST Selection Options The UTF8 LIST selection option tells the server to include mailboxes that only support UTF-8 headers in the output of the list command. The UTF8ONLY LIST selection option tells the server to include all mailboxes that support UTF-8 headers and to exclude mailboxes that don't support UTF-8 headers. Note that UTF8ONLY implies UTF8 so it is not necessary for the client to request both. Use of either selection option will also result in UTF-8 mailbox names in the result as described in Section 3.3 and implies the UTF8 List return option described in Section 3.4.2. 3.4.2. UTF8 LIST Return Option If the client supplies the UTF8 LIST return option, then the server MUST include either the \NoUTF8 or the \UTF8Only mailbox attribute as appropriate. The \NoUTF8 mailbox attribute indicates an attempt to SELECT or EXAMINE that mailbox with the UTF8 parameter will fail with a [NOT-UTF-8] response code. The \UTF8Only mailbox attribute indicates an attempt to SELECT or EXAMINE that mailbox without the UTF8 parameter will fail with a [UTF-8-ONLY] response code. Note that computing this information may be expensive on some server implementations so this return option should not be used unless necessary. The ABNF [RFC5234] for these LIST extensions follows: list-select-independent-opt =/ "UTF8" list-select-base-opt =/ "UTF8ONLY" mbx-list-oflag =/ "\NoUTF8" / "\UTF8Only" return-option =/ "UTF8" resp-text-code =/ "NOT-UTF-8" / "UTF-8-ONLY" Resnick & Newman Expires March 9, 2010 [Page 6] Internet-Draft IMAP Support for UTF-8 September 2009 4. UTF8=APPEND Capability If the UTF8=APPEND capability is advertised, then the server accepts UTF-8 headers in the APPEND command message argument. A client that sends a message with UTF-8 headers to the server MUST send them using the UTF8 APPEND data extension. If the server also advertises the CATENATE capability (as specified in [RFC4469]), the client can use the same data extension to include such a message in a CATENATE message part. The ABNF for the APPEND data extension and CATENATE extension follows: utf8-literal = "UTF8" SP "(" literal8 ")" append-data =/ utf8-literal cat-part =/ utf8-literal A server that advertises UTF8=APPEND has to comply with the requirements of the IMAP base specification and [RFC5322] for message fetching. Mechanisms for 7-bit downgrading to help comply with the standards are discussed in Downgrading mechanism for Internationalized eMail Address (IMA) [RFC5504]. IMAP servers that do not advertise the UTF8=APPEND or UTF8=ONLY capability SHOULD reject an APPEND command that includes any 8-bit in the message headers with a "NO" response. 5. UTF8=USER Capability If the UTF8=USER capability is advertised, that indicates the server accepts UTF-8 user names and passwords and applies SASLprep [RFC4013] to both arguments of the LOGIN command. The server MUST reject UTF-8 that fails to comply with the formal syntax in RFC 3629 [RFC3629]. 6. UTF8=ALL Capability This capability indicates all server mailboxes support UTF-8 headers. Specifically, SELECT and EXAMINE with the UTF8 parameter will never fail with a [NOT-UTF-8] response code. 7. UTF8=ONLY Capability This capability permits an IMAP server to advertise that it does not support the international mailbox name convention (modified UTF-7), and does not permit selection or examination of any mailbox unless Resnick & Newman Expires March 9, 2010 [Page 7] Internet-Draft IMAP Support for UTF-8 September 2009 the UTF8 parameter is provided. As this is an incompatible change to IMAP, a clear warning is necessary. IMAP clients that find implementation of the UTF8 capability problematic are encouraged to at least detect the UTF8=ONLY capability and provide an informative error message to the end-user. When an IMAP mailbox internally uses UTF-8 header native storage, the down-conversion step necessary to permit selection or examination of the mailbox in a backwards compatible fashion will become more difficult to support. Although it is hoped deployed IMAP servers do not advertise UTF8=ONLY for some years, this capability is intended to minimize the disruption when legacy support finally goes away. The UTF8=ONLY capability implies the UTF8 base capability, the UTF8=ALL capability and the UTF8=APPEND capability. A server that advertises UTF8=ONLY need not advertise the three implicit capabilities. 8. Up-Conversion Server Requirements When an IMAP4 server uses a traditional mailbox format that includes 7-bit headers and it chooses to permit access to that mailbox with the UTF8 parameter, it MUST support minimal up-conversion as described in this section. The server MUST support up-conversion of the following address header-fields in the message header: From, Sender, To, CC, Bcc, Resent-From, Resent-Sender, Resent-To, Resent-CC, Resent-Bcc, and Reply-To. This up-conversion MUST include address local-parts in fields downgraded according to [RFC5504], address domains encoded according to IDNA [RFC3490], and MIME header encoding [RFC2047] of display-names and any [RFC5322] comments. The following charsets MUST be supported for up-conversion of MIME header encoding [RFC2047]: UTF-8, US-ASCII, ISO-8859-1, ISO-8859-2, ISO-8859-3, ISO-8859-4, ISO-8859-5, ISO-8859-6, ISO-8859-7, ISO-8859-8, ISO-8859-9, ISO-8859-10, ISO-8859-14, and ISO-8859-15. Other widely deployed MIME charsets SHOULD be supported. Up-conversion of MIME header encoding of the following headers MUST also be implemented: Subject, Date ([RFC5322] comments only), Comments, Keywords, Content-Description. Server implementations also SHOULD up-convert all MIME body headers [RFC2045], SHOULD up-convert or remove the deprecated (and misused) "name" parameter [RFC1341] on Content-Type and MUST up-convert the Content-Disposition [RFC2183] "filename" parameter, except when any Resnick & Newman Expires March 9, 2010 [Page 8] Internet-Draft IMAP Support for UTF-8 September 2009 of these are contained within a multipart/signed MIME body part (see below). These parameters can be encoded using the standard MIME parameter encoding [RFC2231] mechanism, or via non-standard use of MIME header encoding [RFC2047] in quoted strings. The IMAP server MUST NOT perform up-conversion of headers and content of multipart/signed, as well as Original-Recipient and Return-Path. 9. Issues with UTF-8 Header Mailstore When an IMAP server uses a mailbox format that supports UTF-8 headers and it permits selection or examination of that mailbox without the UTF8 parameter, it is the responsibility of the server to comply with the IMAP4rev1 [RFC3501] base specification and [RFC5322] with respect to all header information transmitted over the wire. Mechanisms for 7-bit downgrading to help comply with the standards are discussed in "Downgrading Mechanism for Email Address Internationalization" [RFC5504]. An IMAP server with a mailbox that supports UTF-8 headers MUST comply with the protocol requirements implicit from Section 8. However, the code necessary for such compliance need not be part of the IMAP server itself in this case. For example, the minimal required up- conversion could be performed when a message is inserted into the IMAP-accessible mailbox. 10. IANA Considerations This adds five new capabilities ("UTF8", "UTF8=USER", "UTF8=APPEND", "UTF8=ALL", "UTF8=ONLY") to the IMAP4rev1 capability registry [RFC3501]. This adds two new IMAP4 list selection options and one new IMAP4 list return option. 1. LIST-EXTENDED option name: UTF8 LIST-EXTENDED option type: SELECTION Implied return options(s): UTF8 LIST-EXTENDED option description: Causes the LIST response to include mailboxes that mandate the UTF8 SELECT/EXAMINE parameter. Published specification: RFC XXXX, Section 3.4.1 Resnick & Newman Expires March 9, 2010 [Page 9] Internet-Draft IMAP Support for UTF-8 September 2009 Security considerations: RFC XXXX, Section 11 Intended usage: COMMON Person an email address to contact for further information: see Authors' Addresses at the end of this specification Owner/Change controller: iesg@ietf.org 2. LIST-EXTENDED option name: UTF8ONLY LIST-EXTENDED option type: SELECTION Implied return options(s): UTF8 LIST-EXTENDED option description: Causes the LIST response to include mailboxes that mandate the UTF8 SELECT/EXAMINE parameter and exclude mailboxes that do not support the UTF8 SELECT/EXAMINE parameter. Published specification: RFC XXXX, Section 3.4.1 Security considerations: RFC XXXX, Section 11 Intended usage: COMMON Person an email address to contact for further information: see Authors' Addresses at the end of this specification Owner/Change controller: iesg@ietf.org 3. LIST-EXTENDED option name: UTF8 LIST-EXTENDED option type: RETURN Implied return options(s): none LIST-EXTENDED option description: Causes the LIST response to include \NoUTF8 and \UTF8Only mailbox attributes. Published specification: RFC XXXX, Section 3.4.1 Security considerations: RFC XXXX, Section 11 Intended usage: COMMON Person an email address to contact for further information: see Authors' Addresses at the end of this specification Resnick & Newman Expires March 9, 2010 [Page 10] Internet-Draft IMAP Support for UTF-8 September 2009 Owner/Change controller: iesg@ietf.org 11. Security Considerations The security considerations of UTF-8 [RFC3629] and SASLprep [RFC4013] apply to this specification, particularly with respect to use of UTF-8 in user names and passwords. Otherwise, this is not believed to alter the security considerations of IMAP4rev1. 12. References 12.1. Normative References [RFC1341] Borenstein, N. and N. Freed, "MIME (Multipurpose Internet Mail Extensions): Mechanisms for Specifying and Describing the Format of Internet Message Bodies", RFC 1341, June 1992. [RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies", RFC 2045, November 1996. [RFC2047] Moore, K., "MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text", RFC 2047, November 1996. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC2183] Troost, R., Dorner, S., and K. Moore, "Communicating Presentation Information in Internet Messages: The Content-Disposition Header Field", RFC 2183, August 1997. [RFC2231] Freed, N. and K. Moore, "MIME Parameter Value and Encoded Word Extensions: Character Sets, Languages, and Continuations", RFC 2231, November 1997. [RFC3490] Faltstrom, P., Hoffman, P., and A. Costello, "Internationalizing Domain Names in Applications (IDNA)", RFC 3490, March 2003. [RFC3501] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION 4rev1", RFC 3501, March 2003. [RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO Resnick & Newman Expires March 9, 2010 [Page 11] Internet-Draft IMAP Support for UTF-8 September 2009 10646", STD 63, RFC 3629, November 2003. [RFC4013] Zeilenga, K., "SASLprep: Stringprep Profile for User Names and Passwords", RFC 4013, February 2005. [RFC4466] Melnikov, A. and C. Daboo, "Collected Extensions to IMAP4 ABNF", RFC 4466, April 2006. [RFC4469] Resnick, P., "Internet Message Access Protocol (IMAP) CATENATE Extension", RFC 4469, April 2006. [RFC5161] Gulbrandsen, A. and A. Melnikov, "The IMAP ENABLE Extension", RFC 5161, March 2008. [RFC5198] Klensin, J. and M. Padlipsky, "Unicode Format for Network Interchange", RFC 5198, March 2008. [RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax Specifications: ABNF", STD 68, RFC 5234, January 2008. [RFC5258] Leiba, B. and A. Melnikov, "Internet Message Access Protocol version 4 - LIST Command Extensions", RFC 5258, June 2008. [RFC5322] Resnick, P., Ed., "Internet Message Format", RFC 5322, October 2008. [RFC5335] Abel, Y., "Internationalized Email Headers", RFC 5335, September 2008. [RFC5504] Fujiwara, K. and Y. Yoneya, "Downgrading Mechanism for Email Address Internationalization", RFC 5504, March 2009. 12.2. Informative References [RFC2049] Freed, N. and N. Borenstein, "Multipurpose Internet Mail Extensions (MIME) Part Five: Conformance Criteria and Examples", RFC 2049, November 1996. [RFC2088] Myers, J., "IMAP4 non-synchronizing literals", RFC 2088, January 1997. [RFC2277] Alvestrand, H., "IETF Policy on Character Sets and Languages", BCP 18, RFC 2277, January 1998. [I-D.ietf-eai-pop] Gellens, R. and C. Newman, "POP3 Support for UTF-8", draft-ietf-eai-pop-06 (work in progress), June 2009. Resnick & Newman Expires March 9, 2010 [Page 12] Internet-Draft IMAP Support for UTF-8 September 2009 Appendix A. Design Rationale This non-normative section discusses the reasons behind some of the design choices in the above specification. The basic approach of advertising the ability to access a mailbox in UTF-8 mode is intended to permit graceful upgrade, including servers that support multiple mailbox formats. In particular, it would be undesirable to force conversion of an entire server mailstore to UTF-8 headers, so being able to phase-in support for new mailboxes and gradually migrate old mailboxes is permitted by this design. UTF8=USER is optional because many identity systems are US-ASCII only, so it's helpful to inform the client up-front that UTF-8 won't work. UTF8=APPEND is optional because it effectively requires IMAP server support for down-conversion, which is a much more complex operation than up-conversion. The UTF8=ONLY mechanism simplifies diagnosis of interoperability problems when legacy support goes away. In the situation where backwards compatibility is broken anyway, just-send-UTF-8 IMAP has the advantage that it might work with some legacy clients. However, the difficulty of diagnosing interoperability problems caused by a just-send-UTF-8 IMAP mechanism is the reason the UTF8=ONLY capability mechanism was chosen. The up-conversion requirements are designed to balance the desire to deprecate and eventually eliminate complicated encodings (like MIME header encodings) without creating a significant deployment burden for servers. As IMAP4 servers already require a MIME parser, this includes additional server up-conversion requirements not present in POP3 Support for UTF-8 [I-D.ietf-eai-pop]. The set of mandatory charsets comes from two sources: MIME requirements [RFC2049] and IETF Policy on Character Sets [RFC2277]. Including a requirement to up-convert widely deployed encoded ideographic charsets to UTF-8 would be reasonable for most scenarios, but may require unacceptable table sizes for some embedded devices. The open-ended recommendation to support widely deployed charsets avoids the political ramifications of attempting to list such charsets. The authors believe market forces, existing open-source software, and public conversion tables are sufficient to deploy the appropriate charsets. Resnick & Newman Expires March 9, 2010 [Page 13] Internet-Draft IMAP Support for UTF-8 September 2009 Appendix B. Acknowledgments TBD. Authors' Addresses Pete Resnick Qualcomm Incorporated 5775 Morehouse Drive San Diego, CA 92121-1714 US Phone: +1 858 651 4478 Email: presnick@qualcomm.com URI: http://www.qualcomm.com/~presnick/ Chris Newman Sun Microsystems 3401 Centrelake Dr., Suite 410 Ontario, CA 91761 US Email: chris.newman@sun.com Resnick & Newman Expires March 9, 2010 [Page 14]