imapext-2007
view docs/rfc/rfc2221.txt @ 0:ada5e610ab86
imap-2007e
| author | yuuji@gentei.org |
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| date | Mon, 14 Sep 2009 15:17:45 +0900 |
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7 Network Working Group M. Gahrns
8 Request for Comments: 2221 Microsoft
9 Category: Standards Track October 1997
12 IMAP4 Login Referrals
14 Status of this Memo
16 This document specifies an Internet standards track protocol for the
17 Internet community, and requests discussion and suggestions for
18 improvements. Please refer to the current edition of the "Internet
19 Official Protocol Standards" (STD 1) for the standardization state
20 and status of this protocol. Distribution of this memo is unlimited.
22 Copyright Notice
24 Copyright (C) The Internet Society (1997). All Rights Reserved.
26 1. Abstract
28 When dealing with large amounts of users and many IMAP4 [RFC-2060]
29 servers, it is often necessary to move users from one IMAP4 server to
30 another. For example, hardware failures or organizational changes
31 may dictate such a move.
33 Login referrals allow clients to transparently connect to an
34 alternate IMAP4 server, if their home IMAP4 server has changed.
36 A referral mechanism can provide efficiencies over the alternative
37 'proxy method', in which the local IMAP4 server contacts the remote
38 server on behalf of the client, and then transfers the data from the
39 remote server to itself, and then on to the client. The referral
40 mechanism's direct client connection to the remote server is often a
41 more efficient use of bandwidth, and does not require the local
42 server to impersonate the client when authenticating to the remote
43 server.
45 2. Conventions used in this document
47 In examples, "C:" and "S:" indicate lines sent by the client and
48 server respectively.
50 A home server, is an IMAP4 server that contains the user's inbox.
52 A remote server is a server that contains remote mailboxes.
58 Gahrns Standards Track [Page 1]
60 RFC 2221 IMAP4 Login Referrals October 1997
63 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
64 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
65 document are to be interpreted as described in [RFC-2119].
67 3. Introduction and Overview
69 IMAP4 servers that support this extension MUST list the keyword
70 LOGIN-REFERRALS in their CAPABILITY response. No client action is
71 needed to invoke the LOGIN-REFERRALS capability in a server.
73 A LOGIN-REFERRALS capable IMAP4 server SHOULD NOT return a referral
74 to a server that will return a referral. A client MUST NOT follow
75 more than 10 levels of referral without consulting the user.
77 A LOGIN-REFERRALS response code MUST contain as an argument a valid
78 IMAP server URL as defined in [IMAP-URL].
80 A home server referral consists of either a tagged NO or OK, or an
81 untagged BYE response that contains a LOGIN-REFERRALS response code.
83 Example: A001 NO [REFERRAL IMAP://user;AUTH=*@SERVER2/] Remote Server
85 NOTE: user;AUTH=* is specified as required by [IMAP-URL] to avoid a
86 client falling back to anonymous login.
88 4. Home Server Referrals
90 A home server referral may be returned in response to an AUTHENTICATE
91 or LOGIN command, or it may appear in the connection startup banner.
92 If a server returns a home server referral in a tagged NO response,
93 that server does not contain any mailboxes that are accessible to the
94 user. If a server returns a home server referral in a tagged OK
95 response, it indicates that the user's personal mailboxes are
96 elsewhere, but the server contains public mailboxes which are
97 readable by the user. After receiving a home server referral, the
98 client can not make any assumptions as to whether this was a
99 permanent or temporary move of the user.
101 4.1. LOGIN and AUTHENTICATE Referrals
103 An IMAP4 server MAY respond to a LOGIN or AUTHENTICATE command with a
104 home server referral if it wishes to direct the user to another IMAP4
105 server.
107 Example: C: A001 LOGIN MIKE PASSWORD
108 S: A001 NO [REFERRAL IMAP://MIKE@SERVER2/] Specified user
109 is invalid on this server. Try SERVER2.
114 Gahrns Standards Track [Page 2]
116 RFC 2221 IMAP4 Login Referrals October 1997
119 Example: C: A001 LOGIN MATTHEW PASSWORD
120 S: A001 OK [REFERRAL IMAP://MATTHEW@SERVER2/] Specified
121 user's personal mailboxes located on Server2, but
122 public mailboxes are available.
124 Example: C: A001 AUTHENTICATE GSSAPI
125 <authentication exchange>
126 S: A001 NO [REFERRAL IMAP://user;AUTH=GSSAPI@SERVER2/]
127 Specified user is invalid on this server. Try
128 SERVER2.
130 4.2. BYE at connection startup referral
132 An IMAP4 server MAY respond with an untagged BYE and a REFERRAL
133 response code that contains an IMAP URL to a home server if it is not
134 willing to accept connections and wishes to direct the client to
135 another IMAP4 server.
137 Example: S: * BYE [REFERRAL IMAP://user;AUTH=*@SERVER2/] Server not
138 accepting connections. Try SERVER2
140 5. Formal Syntax
142 The following syntax specification uses the augmented Backus-Naur
143 Form (BNF) as described in [ABNF].
145 This amends the "resp_text_code" element of the IMAP4 grammar
146 described in [RFC-2060]
148 resp_text_code =/ "REFERRAL" SPACE <imapurl>
149 ; See [IMAP-URL] for definition of <imapurl>
150 ; See [RFC-2060] for base definition of resp_text_code
152 6. Security Considerations
154 The IMAP4 login referral mechanism makes use of IMAP URLs, and as
155 such, have the same security considerations as general internet URLs
156 [RFC-1738], and in particular IMAP URLs [IMAP-URL].
158 A server MUST NOT give a login referral if authentication for that
159 user fails. This is to avoid revealing information about the user's
160 account to an unauthorized user.
162 With the LOGIN-REFERRALS capability, it is potentially easier to
163 write a rogue 'password catching' server that collects login data and
164 then refers the client to their actual IMAP4 server. Although
165 referrals reduce the effort to write such a server, the referral
166 response makes detection of the intrusion easier.
170 Gahrns Standards Track [Page 3]
172 RFC 2221 IMAP4 Login Referrals October 1997
175 7. References
177 [RFC-2060], Crispin, M., "Internet Message Access Protocol - Version
178 4rev1", RFC 2060, December 1996.
180 [IMAP-URL], Newman, C., "IMAP URL Scheme", RFC 2192, Innosoft,
181 September 1997.
183 [RFC-1738], Berners-Lee, T., Masinter, L. and M. McCahill, "Uniform
184 Resource Locators (URL)", RFC 1738, December 1994.
186 [RFC-2119], Bradner, S., "Key words for use in RFCs to Indicate
187 Requirement Levels", RFC 2119, March 1997.
189 [ABNF], DRUMS working group, Dave Crocker Editor, "Augmented BNF for
190 Syntax Specifications: ABNF", Work in Progress.
192 8. Acknowledgments
194 Many valuable suggestions were received from private discussions and
195 the IMAP4 mailing list. In particular, Raymond Cheng, Mark Crispin,
196 Mark Keasling Chris Newman and Larry Osterman made significant
197 contributions to this document.
199 9. Author's Address
201 Mike Gahrns
202 Microsoft
203 One Microsoft Way
204 Redmond, WA, 98072
206 Phone: (206) 936-9833
207 EMail: mikega@microsoft.com
226 Gahrns Standards Track [Page 4]
228 RFC 2221 IMAP4 Login Referrals October 1997
231 10. Full Copyright Statement
233 Copyright (C) The Internet Society (1997). All Rights Reserved.
235 This document and translations of it may be copied and furnished to
236 others, and derivative works that comment on or otherwise explain it
237 or assist in its implmentation may be prepared, copied, published
238 andand distributed, in whole or in part, without restriction of any
239 kind, provided that the above copyright notice and this paragraph are
240 included on all such copies and derivative works. However, this
241 document itself may not be modified in any way, such as by removing
242 the copyright notice or references to the Internet Society or other
243 Internet organizations, except as needed for the purpose of
244 developing Internet standards in which case the procedures for
245 copyrights defined in the Internet Standards process must be
246 followed, or as required to translate it into languages other than
247 English.
249 The limited permissions granted above are perpetual and will not be
250 revoked by the Internet Society or its successors or assigns.
252 This document and the information contained herein is provided on an
253 "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
254 TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
255 BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
256 HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
257 MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE."
282 Gahrns Standards Track [Page 5]