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Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) ** Obsolete normative reference: RFC 3501 (Obsoleted by RFC 9051) -- Obsolete informational reference (is this intentional?): RFC 3348 (Obsoleted by RFC 5258) Summary: 1 error (**), 0 flaws (~~), 2 warnings (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group B. Leiba, Ed. 3 Internet-Draft Huawei Technologies 4 Intended status: Standards Track February 25, 2018 5 Expires: August 27, 2018 7 IMAP $Important Keyword and \Important Special-Use Attribute 8 draft-leiba-extra-specialuse-important-01 10 Abstract 12 RFC 6154 created an IMAP Special-Use LIST extension and defined an 13 initial set of attributes. This document defines a new attribute, 14 "\Important", and establishes a new IANA registry for IMAP folder 15 attributes, registering the attributes defined in RFCs 3348, 3501, 16 and 6154. This document also defines a new IMAP keyword, 17 "$Important", and registers it in the registry defined in RFC 5788. 19 Status of this Memo 21 This Internet-Draft is submitted in full conformance with the 22 provisions of BCP 78 and BCP 79. 24 Internet-Drafts are working documents of the Internet Engineering 25 Task Force (IETF). Note that other groups may also distribute 26 working documents as Internet-Drafts. The list of current Internet- 27 Drafts is at http://datatracker.ietf.org/drafts/current/. 29 Internet-Drafts are draft documents valid for a maximum of six months 30 and may be updated, replaced, or obsoleted by other documents at any 31 time. It is inappropriate to use Internet-Drafts as reference 32 material or to cite them other than as "work in progress." 34 This Internet-Draft will expire on August 27, 2018. 36 Copyright Notice 38 Copyright (c) 2018 IETF Trust and the persons identified as the 39 document authors. All rights reserved. 41 This document is subject to BCP 78 and the IETF Trust's Legal 42 Provisions Relating to IETF Documents (http://trustee.ietf.org/ 43 license-info) in effect on the date of publication of this document. 44 Please review these documents carefully, as they describe your rights 45 and restrictions with respect to this document. Code Components 46 extracted from this document must include Simplified BSD License text 47 as described in Section 4.e of the Trust Legal Provisions and are 48 provided without warranty as described in the Simplified BSD License. 50 Table of Contents 52 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2 53 1.1. Conventions used in this document . . . . . . . . . . . . . 2 54 2. Definition of the '$Important' Message Keyword . . . . . . . . 2 55 3. Definition of the 'Important' Mailbox Attribute . . . . . . . 3 56 3.1. Formal Syntax . . . . . . . . . . . . . . . . . . . . . . . 3 57 3.2. Example . . . . . . . . . . . . . . . . . . . . . . . . . . 3 58 4. Implementation Notes . . . . . . . . . . . . . . . . . . . . . 4 59 5. Security Considerations . . . . . . . . . . . . . . . . . . . 4 60 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 61 6.1. Registration of the $Important keyword . . . . . . . . . . . 5 62 6.2. Creation of the IMAP Mailbox Name Attributes Registry . . . 6 63 6.2.1. Instructions to the Designated Expert . . . . . . . . . . 6 64 6.3. Initial Entries for the IMAP Mailbox Name Attributes Registry 6 65 7. Changes During Document Development . . . . . . . . . . . . . 7 66 8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 8 67 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8 68 9.1. Normative References . . . . . . . . . . . . . . . . . . . . 8 69 9.2. Informative References . . . . . . . . . . . . . . . . . . . 8 70 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 9 72 1. Introduction 74 The Internet Message Access Protocol (IMAP) specification [RFC3501] 75 defines the use of message keywords, and an IMAP Keywords registry is 76 created in [RFC5788]. [RFC6154] defines an extension to the IMAP 77 LIST command for special-use mailboxes. The extension allows servers 78 to provide extra information (attributes) about the purpose of a 79 mailbox and defines an initial set of special-use attributes. 81 This document does the following: 83 o Defines a new message keyword, "$Important", to apply to messages 84 that are considered important for the user, by some externally 85 defined criteria. 87 o Registers the "$Important" keyword in the IMAP Keywords registry. 89 o Defines a new special-use attribute, "\Important", to designate a 90 mailbox that will hold messages that are considered important for 91 the user, by some externally defined criteria. 93 o Creates a registry for IMAP mailbox attributes and registers the 94 new attribute and those defined in [RFC3348], [RFC3501], and 95 [RFC6154]. 97 1.1. Conventions used in this document 99 In examples, "C:" indicates lines sent by a client that is connected 100 to a server. "S:" indicates lines sent by the server to the client. 102 2. Definition of the '$Important' Message Keyword 103 The "$Important" keyword is a signal that a message is likely 104 important to the user. The keyword is generally expected to be set 105 automatically by the system based on available signals (such as who 106 the message is from, who else the message is addressed to, evaluation 107 of the subject or content, or other heuristics). While the keyword 108 also can be set by the user, that is not expected to be the primary 109 usage. 111 This is distinct from the "\Flagged" system flag in two ways: 113 1. "$Important" carries a specific meaning of general importance, as 114 opposed to follow-up or urgency. It is meant to be used for a 115 form of triage, with "\Flagged" remaining as a designation of 116 special attention, need for follow-up, or time-sensitivity. In 117 particular, the sense of "$Important" is that other messages that 118 are "like this one" according to some server-applied heuristics 119 will also be $Important. 121 2. The setting of "$Important" is expected to be based at least 122 partly on heuristics, generally set automatically by the server, 123 whereas "\Flagged" is only intended to be set by the user with 124 some sort of "flag this message" or "put a star on this message" 125 interface. 127 3. Definition of the 'Important' Mailbox Attribute 129 The "\Important" mailbox attribute is a signal that the mailbox 130 contains messages that are likely important to the user. In an 131 implementation that also supports the "$Important" keyword, this 132 special use is likely to represent a virtual mailbox collecting 133 messages (from other mailboxes) that are marked with the "$Important" 134 keyword. In other implementations, the system might automatically 135 put messages there based on the same sorts of heuristics that are 136 noted for the "$Important" keyword (see Section 2). The distinction 137 between "\Important" and "\Flagged" for mailboxes is similar to those 138 between "$Important" and "\Flagged" for messages. 140 3.1. Formal Syntax 142 The following syntax specification adds to the one in [RFC6154], 143 Section 6, using Augmented Backus-Naur Form (ABNF) as described in 144 [RFC5234]. Be sure to see the ABNF notes at the beginning of 145 [RFC3501], Section 9. 147 use-attr =/ "\Important" 149 3.2. Example 151 In the following example, the mailbox called "Important Messages" is 152 the one designated with the "\Important" attribute. 154 C: t1 list "" "Imp*" 155 S: * LIST (\HasNoChildren \Important) "/" "Important Messages" 156 S: * LIST (\HasNoChildren) "/" "Imported Wine" 157 S: t1 OK Success 159 4. Implementation Notes 161 This section is non-normative and is intended to describe the 162 intended (and current as of this publication) usage of "$Important" 163 in contrast with "\Flagged" on a message. 165 On the server: 167 o \Flagged is set or cleared in response to an explicit command from 168 the client. 170 o $Important is set via a heuristic process performed by the server, 171 usually involving analysis of header fields, what mailbox the 172 message is filed in, perhaps message content, attachments, and 173 such. It may then be set or cleared in response to an explicit 174 command from the client, and the server may use that to adjust the 175 heuristics in the future. It's also possible that the server will 176 re-evaluate this and make a message $Important later if the user 177 accesses the message frequently, for example. 179 On the client: 181 o Typically, an icon such as a flag or a star, or an indication such 182 as red or bold text, is associated with \Flagged, and the UI 183 provides a way for the user to turn that icon or indication on or 184 off. Manipulation of the this results in a command to the server. 186 o Typically, a lesser indication is used for $Important. The client 187 might or might not provide the user with a way to manipulate it. 188 If it does, manipulation results in a command to the server. 190 5. Security Considerations 192 The security considerations in [RFC6154], Section 7, apply equally to 193 this extension. In particular, "Conveying special-use information to 194 a client exposes a small bit of extra information that could be of 195 value to an attacker." Moreover, identifying "important" messages or 196 a place where important messages are kept could give an attacker a 197 strategic starting point. If the algorithm by which messages are 198 determined to be important is well known, still more information is 199 exposed -- perhaps, for example, there is an implication that the 200 senders of these messages are particularly significant to the mailbox 201 owner, and perhaps that is information that should not be made 202 public. 204 As noted in RFC 6154, it is wise to protect the IMAP channel from 205 passive eavesdropping, and to defend against unauthorized discernment 206 of the identity of a user's "\Important" mailbox or of a user's 207 "$Important" messages. 209 6. IANA Considerations 211 This document contains 3 actions for IANA, specified in the sections 212 below: 214 1. Registration of the "$Important" keyword. 216 2. Creation of a new "IMAP Mailbox Name Attributes" registry. 218 3. Registration of initial entries in the "IMAP Mailbox Name 219 Attributes" registry. 221 6.1. Registration of the $Important keyword 223 IANA is asked to register the $Important keyword in the "IMAP 224 Keywords" registry, as follows, using the template in [RFC5788]. 226 IMAP keyword name: $Important 228 Purpose (description): The "$Important" keyword is a signal that a 229 message is likely important to the user. 231 Private or Shared on a server: PRIVATE 233 Is it an advisory keyword or may it cause an automatic action: 234 Advisory (but see the reference for details). 236 When/by whom the keyword is set/cleared: The keyword can be set by 237 the user, or automatically by the system based on available 238 signals (such as who the message is from, who else the message 239 is addressed to, evaluation of the subject or content, or other 240 heuristics). 242 Related keywords: None (but see the reference for the related mailbox 243 name attribute). 245 Related IMAP capabilities: None. 247 Security considerations: See [[THIS RFC]], Section 5 249 Published specification: [[THIS RFC]] 251 Person & email address to contact for further information: 252 IETF Applications and Real-Time Area 254 Intended usage: COMMON 255 Owner/Change controller: IESG 257 Note: None. 259 6.2. Creation of the IMAP Mailbox Name Attributes Registry 261 IANA is asked to create a new registry in the group "Internet Message 262 Access Protocol (IMAP)". The new registry will be called "IMAP 263 Mailbox Name Attributes", and will have two references: "RFC 3501, 264 Section 7.2.2", and "[[THIS RFC]], Section 6". 266 The registry entries will contain three fields: 268 1. Attribute Name 270 2. Description 272 3. Reference 274 IANA will keep this list in alphabetical order by Attribute Name, 275 which is registered without the initial backslash ("\"). The names 276 are generally registered with initial capital letters, but are 277 treated as case-insensitive strings. 279 The registration policy for the new registry will be listed as "IETF 280 Review or Expert Review" [RFC8126], and new registrations will be 281 accepted in one of two ways: 283 1. For registrations requested in an IETF consensus document, the 284 registration policy will be IETF Review, and the request will be 285 made in the IANA Considerations section of the document, giving 286 the requested values for each of the three fields. 288 2. For other registrations, the policy will be Expert Review policy 289 (see Section 6.2.1), and the request will be made by sending 290 email to IANA asking for a new IMAP Mailbox Name Attribute and 291 giving the requested values for each of the three fields. 293 6.2.1. Instructions to the Designated Expert 295 The expert reviewer, who will be designated by the IESG, is expected 296 to provide only a general review of the requested registration, 297 checking that the reference and description are adequate for 298 understanding the intent of the registered attribute. Efforts should 299 also be made to generalize the intent of an attribute so that 300 multiple implementations with the same requirements may reuse 301 existing attributes. Except for this check, this is intended to be 302 very close to a first come first served policy, and the expert should 303 not block serious registration requests with a reasonable reference. 304 The reference may be to any form of documentation, including a web 305 page, but consideration should be given to providing one that is 306 expected to be long-lived and stable. 308 6.3. Initial Entries for the IMAP Mailbox Name Attributes Registry 309 The registry will initially contain these entries: 311 +===============+===================================+===========+ 312 | Attribute | Description | Reference | 313 | Name | | | 314 +===============+===================================+===========+ 315 | All | All messages | [RFC6154] | 316 +---------------+-----------------------------------+-----------+ 317 | Archive | Archived messages | [RFC6154] | 318 +---------------+-----------------------------------+-----------+ 319 | Drafts | Messages that are working drafts | [RFC6154] | 320 +---------------+-----------------------------------+-----------+ 321 | Flagged | Messages with the \Flagged flag | [RFC6154] | 322 +---------------+-----------------------------------+-----------+ 323 | HasChildren | Has accessible child mailboxes | [RFC3348] | 324 +---------------+-----------------------------------+-----------+ 325 | HasNoChildren | Has no accessible child mailboxes | [RFC3348] | 326 +---------------+-----------------------------------+-----------+ 327 | Important | Messages deemed important to user | THIS RFC | 328 +---------------+-----------------------------------+-----------+ 329 | Junk | Messages identified as Spam/Junk | [RFC6154] | 330 +---------------+-----------------------------------+-----------+ 331 | Marked | Server has marked the mailbox as | [RFC3501] | 332 | | "interesting" | | 333 +---------------+-----------------------------------+-----------+ 334 | NoInferiors | No hierarchy under this name | [RFC3501] | 335 +---------------+-----------------------------------+-----------+ 336 | Noselect | The mailbox is not selectable | [RFC3501] | 337 +---------------+-----------------------------------+-----------+ 338 | Sent | Sent mail | [RFC6154] | 339 +---------------+-----------------------------------+-----------+ 340 | Trash | Messages the user has discarded | [RFC6154] | 341 +---------------+-----------------------------------+-----------+ 342 | Unmarked | No new messages since last select | [RFC3501] | 343 +===============+===================================+===========+ 345 7. Changes During Document Development 347 [[RFC Editor: Please remove this section prior to publication.]] 349 Changes in draft-leiba-extra-specialuse-important-01 351 o Updated "IETF Applications Area" to "IETF Applications and Real- 352 Time Area". 354 o Changed some wording to make the distinction between \Flagged and 355 \Important clearer. 357 o Added some text explaining how \Important is used in existing 358 servers. 360 o Added a note in the ABNF section referring to the ABNF notes in 361 the IMAP spec. 363 Changes in draft-leiba-extra-specialuse-important-00 365 o Reset status, moved Eric to "Contributors", changed Barry to 366 "Editor" 368 o Updated BCP 26 reference to RFC 8126. 370 Changes in draft-iceman-imap-specialuse-important-02 372 o Added the definition and registration of $Important. 374 o Noted that \Important might be implemented as a virtual collection 375 of $Important messages. 377 Changes in draft-iceman-imap-specialuse-important-01 379 o Expanded the new registry to all mailbox name attributes, and 380 added the attributes from 3501 and 3348 (suggested by Alexey). 381 This also adds those two documents to the "updates" list. 383 o Recorded Cyrus's suggestion to define $Important. 385 8. Contributors 387 The following author was an original contributor to this document in 388 addition to the editor. 390 Eric "Iceman" 391 Google 392 iceman@google.com 394 9. References 396 9.1. Normative References 398 [RFC3501] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION 399 4rev1", RFC 3501, March 2003. 401 [RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax 402 Specifications: ABNF", STD 68, RFC 5234, January 2008. 404 [RFC6154] Leiba, B. and J. Nicolson, "IMAP LIST Extension for 405 Special-Use Mailboxes", RFC 6154, March 2011. 407 [RFC8126] Cotton, M., Leiba, B. and T. Narten, "Guidelines for 408 Writing an IANA Considerations Section in RFCs", BCP 26, 409 RFC 8126, DOI 10.17487/RFC8126, June 2017, . 412 9.2. Informative References 414 [RFC3348] Gahrns, M. and R. Cheng, "The Internet Message Action 415 Protocol (IMAP4) Child Mailbox Extension", RFC 3348, July 416 2002. 418 [RFC5788] Melnikov, A. and D. Cridland, "IMAP4 Keyword Registry", 419 RFC 5788, March 2010. 421 Author's Address 423 Barry Leiba, editor 424 Huawei Technologies 426 Phone: +1 646 827 0648 427 Email: barryleiba@computer.org 428 URI: http://internetmessagingtechnology.org/