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Gondwana, Ed. 3 Internet-Draft FastMail 4 Updates: 3501 (if approved) July 31, 2018 5 Intended status: Standards Track 6 Expires: February 1, 2019 8 IMAP Extension for object identifiers 9 draft-ietf-extra-imap-objectid-07 11 Abstract 13 This document updates RFC3501 (IMAP4rev1) with persistent identifiers 14 on mailboxes and messages to allow clients to more efficiently re-use 15 cached data when resources have changed location on the server. 17 Status of This Memo 19 This Internet-Draft is submitted in full conformance with the 20 provisions of BCP 78 and BCP 79. 22 Internet-Drafts are working documents of the Internet Engineering 23 Task Force (IETF). Note that other groups may also distribute 24 working documents as Internet-Drafts. The list of current Internet- 25 Drafts is at https://datatracker.ietf.org/drafts/current/. 27 Internet-Drafts are draft documents valid for a maximum of six months 28 and may be updated, replaced, or obsoleted by other documents at any 29 time. It is inappropriate to use Internet-Drafts as reference 30 material or to cite them other than as "work in progress." 32 This Internet-Draft will expire on February 1, 2019. 34 Copyright Notice 36 Copyright (c) 2018 IETF Trust and the persons identified as the 37 document authors. All rights reserved. 39 This document is subject to BCP 78 and the IETF Trust's Legal 40 Provisions Relating to IETF Documents 41 (https://trustee.ietf.org/license-info) in effect on the date of 42 publication of this document. Please review these documents 43 carefully, as they describe your rights and restrictions with respect 44 to this document. Code Components extracted from this document must 45 include Simplified BSD License text as described in Section 4.e of 46 the Trust Legal Provisions and are provided without warranty as 47 described in the Simplified BSD License. 49 Table of Contents 51 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 52 2. Conventions Used In This Document . . . . . . . . . . . . . . 3 53 3. CAPABILITY Identification . . . . . . . . . . . . . . . . . . 3 54 4. MAILBOXID object identifier . . . . . . . . . . . . . . . . . 3 55 4.1. New response code for CREATE . . . . . . . . . . . . . . 4 56 4.2. New OK Untagged Response for SELECT and EXAMINE . . . . . 4 57 4.3. New attribute for STATUS . . . . . . . . . . . . . . . . 5 58 5. EMAILID object identifier and THREADID correlator . . . . . . 6 59 5.1. EMAILID identifier for identical messages . . . . . . . . 6 60 5.2. THREADID identifer for related messages . . . . . . . . . 6 61 5.3. New Message Data Items in FETCH and UID FETCH Commands . 7 62 6. New Filters on SEARCH command . . . . . . . . . . . . . . . . 9 63 7. Formal syntax . . . . . . . . . . . . . . . . . . . . . . . . 9 64 8. Implementation considerations . . . . . . . . . . . . . . . . 10 65 8.1. Assigning object identifiers . . . . . . . . . . . . . . 10 66 8.2. Interaction with special cases . . . . . . . . . . . . . 11 67 8.3. Client usage . . . . . . . . . . . . . . . . . . . . . . 11 68 9. Future considerations . . . . . . . . . . . . . . . . . . . . 12 69 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12 70 11. Security Considerations . . . . . . . . . . . . . . . . . . . 12 71 12. Changes . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 72 12.1. draft-ietf-extra-imap-objectid-07 . . . . . . . . . . . 13 73 12.2. draft-ietf-extra-imap-objectid-06 . . . . . . . . . . . 13 74 12.3. draft-ietf-extra-imap-objectid-05 . . . . . . . . . . . 13 75 12.4. draft-ietf-extra-imap-objectid-04 . . . . . . . . . . . 13 76 12.5. draft-ietf-extra-imap-objectid-03 . . . . . . . . . . . 14 77 12.6. draft-ietf-extra-imap-objectid-02 . . . . . . . . . . . 14 78 12.7. draft-ietf-extra-imap-objectid-01 . . . . . . . . . . . 14 79 12.8. draft-ietf-extra-imap-objectid-00 . . . . . . . . . . . 15 80 12.9. draft-ietf-extra-imap-uniqueid-00 . . . . . . . . . . . 15 81 12.10. draft-gondwana-imap-uniqueid-01 . . . . . . . . . . . . 15 82 12.11. draft-gondwana-imap-uniqueid-00 . . . . . . . . . . . . 15 83 13. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 15 84 13.1. Appendix 1: ideas for implementing object identifiers . 16 85 14. References . . . . . . . . . . . . . . . . . . . . . . . . . 16 86 14.1. Normative References . . . . . . . . . . . . . . . . . . 16 87 14.2. Informative References . . . . . . . . . . . . . . . . . 17 88 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 18 90 1. Introduction 92 IMAP stores are often used by many clients. Each client may cache 93 data from the server so that they don't need to re-download 94 information. [RFC3501] defines that a mailbox can be uniquely 95 referenced by its name and UIDVALIDITY, and a message within that 96 mailbox can be uniquely referenced by its mailbox (name + 97 UIDVALIDITY) and UID. The triple of mailbox name, UIDVALIDITY and 98 UID is guaranteed to be immutable. 100 [RFC4315] defines a COPYUID response which allows a client which 101 copies messages to know the mapping between the UIDs in the source 102 and destination mailboxes, and hence update its local cache. 104 If a mailbox is successfully renamed by a client, that client will 105 know that the same messages exist in the destination mailbox name as 106 previously existed in the source mailbox name. 108 The result is that the client which copies (or [RFC6851] moves) 109 messages or renames a mailbox can update its local cache, but any 110 other client connected to the same store can not know with certainty 111 that the messages are identical, and so will re-download everything. 113 This extension adds new properties to a message (EMAILID) and mailbox 114 (MAILBOXID) which allow a client to quickly identify messages or 115 mailboxes which have been renamed by another client. 117 This extension also adds an optional thread identifier (THREADID) to 118 messages, which can be used by the server to indicate messages which 119 it has identified to be related. A server that does not implement 120 threading will return NIL to all requests for THREADID. 122 2. Conventions Used In This Document 124 In examples, "C:" indicates lines sent by a client that is connected 125 to a server. "S:" indicates lines sent by the server to the client. 127 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 128 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 129 "OPTIONAL" in this document are to be interpreted as described in BCP 130 14 [RFC2119] [RFC8174] when, and only when, they appear in all 131 capitals, as shown here. 133 3. CAPABILITY Identification 135 IMAP servers that support this extension MUST include "OBJECTID" in 136 the response list to the CAPABILITY command. 138 4. MAILBOXID object identifier 140 The MAILBOXID is a server-allocated unique identifer for each 141 mailbox. 143 The server MUST return the same MAILBOXID for a mailbox with the same 144 name and UIDVALIDITY. 146 The server MUST NOT report the same MAILBOXID for two mailboxes at 147 the same time. 149 The server MUST NOT reuse the same MAILBOXID for a mailbox which does 150 not obey all the invariants that [RFC3501] defines for a mailbox 151 which does not change name or UIDVALIDITY. 153 The server MUST keep the same MAILBOXID for the source and 154 destination when renaming a mailbox in a way which keeps the same 155 messages (but see [RFC3501] for the special case regarding renaming 156 of INBOX, which is treated as creating a new mailbox and moving the 157 messages) 159 4.1. New response code for CREATE 161 This document extends the CREATE command to have the response code 162 MAILBOXID on successful mailbox creation. 164 A server advertising the OBJECTID capability MUST include the 165 MAILBOXID response code in the tagged OK response to all successful 166 CREATE commands. 168 Syntax: "MAILBOXID" SP "(" ")" 170 Response code in tagged OK for successful CREATE command. 172 Example: 174 C: 3 create foo 175 S: 3 OK [MAILBOXID (F2212ea87-6097-4256-9d51-71338625)] Completed 176 C: 4 create bar 177 S: 4 OK [MAILBOXID (F6352ae03-b7f5-463c-896f-d8b48ee3)] Completed 178 C: 5 create foo 179 S: 5 NO Mailbox already exists 181 4.2. New OK Untagged Response for SELECT and EXAMINE 183 This document adds a new untagged response code to the SELECT and 184 EXAMINE commands. 186 A server advertising the OBJECTID capability MUST return an untagged 187 OK response with the MAILBOXID response code on all successful SELECT 188 and EXAMINE commands. 190 Syntax: "OK" SP "[" "MAILBOXID" SP "(" ")" "]" text 192 Untagged OK response to SELECT or EXAMINE. 194 Example: 196 C: 27 select "foo" 197 [...] 198 S: * OK [MAILBOXID (F2212ea87-6097-4256-9d51-71338625)] Ok 199 [...] 200 S: 27 OK [READ-WRITE] Completed 202 4.3. New attribute for STATUS 204 This document adds the MAILBOXID attribute to the STATUS command 205 using the extended syntax defined in [RFC4466]. 207 A server that advertises the OBJECTID capability MUST support the 208 MAILBOXID status attribute. 210 Syntax: "MAILBOXID" 212 The attribute in the STATUS command. 214 Syntax: "MAILBOXID" SP "(" ")" 216 The response item in the STATUS response contains the objectid 217 assigned by the server for this mailbox. 219 Example: 221 C: 6 status foo (mailboxid) 222 S: * STATUS foo (MAILBOXID (F2212ea87-6097-4256-9d51-71338625)) 223 S: 6 OK Completed 224 C: 7 status bar (mailboxid) 225 S: * STATUS bar (MAILBOXID (F6352ae03-b7f5-463c-896f-d8b48ee3)) 226 S: 7 OK Completed 227 C: 8 rename foo renamed 228 S: * OK rename foo renamed 229 S: 8 OK Completed 230 C: 9 status renamed (mailboxid) 231 S: * STATUS renamed (MAILBOXID (F2212ea87-6097-4256-9d51-71338625)) 232 S: 9 OK Completed 233 C: 10 status bar (mailboxid) 234 S: * STATUS bar (MAILBOXID (F6352ae03-b7f5-463c-896f-d8b48ee3)) 235 S: 10 OK Completed 237 When the LIST-STATUS IMAP capability defined in [RFC5819] is also 238 available, the STATUS command can be combined with the LIST command. 240 Example: 242 C: 11 list "" "*" return (status (mailboxid)) 243 S: * LIST (\HasNoChildren) "." INBOX 244 S: * STATUS INBOX (MAILBOXID (Ff8e3ead4-9389-4aff-adb1-d8d89efd8cbf)) 245 S: * LIST (\HasNoChildren) "." bar 246 S: * STATUS bar (MAILBOXID (F6352ae03-b7f5-463c-896f-d8b48ee3)) 247 S: * LIST (\HasNoChildren) "." renamed 248 S: * STATUS renamed (MAILBOXID (F2212ea87-6097-4256-9d51-71338625)) 249 S: 11 OK Completed (0.001 secs 3 calls) 251 5. EMAILID object identifier and THREADID correlator 253 5.1. EMAILID identifier for identical messages 255 The EMAILID data item is an objectid which uniquely identifies the 256 content of a single message. Anything which must remain immutable on 257 a {name, uidvalidity, uid} triple must also be the same between 258 messages with the same EMAILID. 260 The server MUST return the same EMAILID for the same triple, hence 261 EMAILID is immutable. 263 The server MUST return the same EMAILID as the source message for the 264 matching destination message in the COPYUID pairing after a COPY or 265 [RFC6851] MOVE command. 267 The server MAY assign the same EMAILID as an existing message upon 268 APPEND (e.g. if it detects that the new message has exactly identical 269 content to that of an existing message) 271 NOTE: EMAILID only identifies the immutable content of the message. 272 In particular, it is possible for different messages with the same 273 EMAILID to have different keywords. This document does not specify a 274 way to STORE by EMAILID. 276 5.2. THREADID identifer for related messages 278 The THREADID data item is an objectid which uniquely identifies a set 279 of messages which the server believes should be grouped together when 280 presented. 282 THREADID calculation is generally based on some combination of 283 References, In-Reply-To and Subject, but the exact logic is left up 284 to the server implementation. [RFC5256] describes some algorithms 285 that could be used, however this specfication does not mandate any 286 particular strategy. 288 The server MUST return the same THREADID for all messages with the 289 same EMAILID. 291 The server SHOULD return the same THREADID for related messages even 292 if they are in different mailboxes. 294 The server MUST NOT change the THREADID of a message once reported. 296 THREADID is optional, if the server doesn't support THREADID or is 297 unable to calculate relationships between messages, it MUST return 298 NIL to all FETCH responses for the THREADID data item, and a SEARCH 299 for THREADID MUST NOT match any messages. 301 The server MUST NOT use the same objectid value for both EMAILIDs and 302 THREADIDs. If they are stored with the same value internally, the 303 server can generate prefixed values (as shown in the examples below 304 with M and T prefixes) to avoid clashes. 306 5.3. New Message Data Items in FETCH and UID FETCH Commands 308 This document defines two FETCH items: 310 Syntax: EMAILID 312 The EMAILID message data item causes the server to return EMAILID 313 FETCH response data items. 315 Syntax: THREADID 317 The THREADID message data item causes the server to return THREADID 318 FETCH response data items. 320 And the following responses: 322 Syntax: EMAILID ( ) 324 The EMAILID response data item contains the server-assigned objectid 325 for each message. 327 Syntax: THREADID ( ) 329 The THREADID response data item contains the server-assigned objectid 330 for the set of related messages to which this message belongs. 332 Syntax: THREADID NIL 334 The NIL value to the THREADID response data item is returned when 335 the server mailbox does not support THREADID calculation. 337 Example: 339 C: 5 append inbox "20-Mar-2018 03:07:37 +1100" {733} 340 [...] 341 Subject: Message A 342 Message-ID: 343 [...] 344 S: 5 OK [APPENDUID 1521475658 1] Completed 346 C: 11 append inbox "20-Mar-2018 03:07:37 +1100" {793} 347 [...] 348 Subject: Re: Message A 349 Message-ID: 350 References: 351 [...] 352 S: 11 OK [APPENDUID 1521475658 2] Completed 354 C: 17 append inbox "20-Mar-2018 03:07:37 +1100" {736} 355 [...] 356 Subject: Message C 357 Message-ID: 358 [...] 359 S: 17 OK [APPENDUID 1521475658 3] Completed 361 C: 22 fetch 1:* (emailid threadid) 362 S: * 1 FETCH (EMAILID (M6d99ac3275bb4e) THREADID (T64b478a75b7ea9)) 363 S: * 2 FETCH (EMAILID (M288836c4c7a762) THREADID (T64b478a75b7ea9)) 364 S: * 3 FETCH (EMAILID (M5fdc09b49ea703) THREADID (T11863d02dd95b5)) 365 S: 22 OK Completed (0.000 sec) 367 C: 23 move 2 foo 368 S: * OK [COPYUID 1521475659 2 1] Completed 369 S: * 2 EXPUNGE 370 S: 23 OK Completed 372 C: 24 fetch 1:* (emailid threadid) 373 S: * 1 FETCH (EMAILID (M6d99ac3275bb4e) THREADID (T64b478a75b7ea9)) 374 S: * 2 FETCH (EMAILID (M5fdc09b49ea703) THREADID (T11863d02dd95b5)) 375 S: 24 OK Completed (0.000 sec) 376 C: 25 select "foo" 378 C: 25 select "foo" 379 [...] 380 S: 25 OK [READ-WRITE] Completed 381 C: 26 fetch 1:* (emailid threadid) 382 S: * 1 FETCH (EMAILID (M288836c4c7a762) THREADID (T64b478a75b7ea9)) 383 S: 26 OK Completed (0.000 sec) 385 Example: (no THREADID support) 386 C: 26 fetch 1:* (emailid threadid) 387 S: * 1 FETCH (EMAILID (M00000001) THREADID NIL) 388 S: * 2 FETCH (EMAILID (M00000002) THREADID NIL) 389 S: 26 OK Completed (0.000 sec) 391 6. New Filters on SEARCH command 393 This document defines filters EMAILID and THREADID on the SEARCH 394 command. 396 EMAILID 398 Messages whose EMAILID is exactly the specified objectid. 400 THREADID 402 Messages whose THREADID is exactly the specified objectid. 404 Example: (as if run before the MOVE above when the mailbox had 3 405 messages) 407 C: 27 search emailid M6d99ac3275bb4e 408 S: * SEARCH 1 409 S: 27 OK Completed (1 msgs in 0.000 secs) 410 C: 28 search threadid T64b478a75b7ea9 411 S: * SEARCH 1 2 412 S: 28 OK Completed (2 msgs in 0.000 secs) 414 7. Formal syntax 416 The following syntax specification uses the Augmented Backus-Naur 417 Form (ABNF) [RFC5234] notation. Elements not defined here can be 418 found in the formal syntax of the ABNF [RFC5234], IMAP [RFC3501], and 419 IMAP ABNF extensions [RFC4466] specifications. 421 Except as noted otherwise, all alphabetic characters are case- 422 insensitive. The use of upper- or lowercase characters to define 423 token strings is for editorial clarity only. Implementations MUST 424 accept these strings in a case-insensitive fashion. 426 capability =/ "OBJECTID" 428 fetch-att =/ "EMAILID" / "THREADID" 430 fetch-emailid-resp = "EMAILID" SP "(" objectid ")" 431 ; follows tagged-ext production from [@!RFC4466] 433 fetch-threadid-resp = "THREADID" SP ( "(" objectid ")" / nil ) 434 ; follows tagged-ext production from [@!RFC4466] 436 msg-att-static =/ fetch-emailid-resp / fetch-threadid-resp 438 objectid = 1*255(ALPHA / DIGIT / "_" / "-") 439 ; characters in object identifiers are case 440 ; significant 442 resp-text-code =/ "MAILBOXID" SP "(" objectid ")" 443 ; incorporated before the expansion rule of 444 ; atom [SP 1*<any TEXT-CHAR except "]">] 445 ; that appears in [@!RFC3501] 447 search-key =/ "EMAILID" SP objectid / "THREADID" SP objectid 449 status-att =/ "MAILBOXID" 451 status-att-value =/ "MAILBOXID" SP "(" objectid ")" 452 ; follows tagged-ext production from [@!RFC4466] 454 8. Implementation considerations 456 8.1. Assigning object identifiers 458 All objectid values are allocated by the server. 460 In the interests of reducing the possibilities of encoding mistakes, 461 objectids are restricted to a safe subset of possible byte values, 462 and in order to allow clients to allocate storage, they are 463 restricted in length. 465 An objectid is a string of 1 to 255 characters from the following set 466 of 64 codepoints. a-z, A-Z, 0-9, '_', '-'. These characters are safe 467 to use in almost any context (e.g. filesystems, URIs, IMAP atoms). 469 For maximum safety, servers should also follow defensive allocation 470 strategies to avoid creating risks where glob completion or data type 471 detection may be present (e.g. on filesystems or in spreadsheets). 472 In particular it is wise to avoid: 474 o ids starting with - 476 o ids starting with digits 478 o ids which contain only digits 480 o ids which differ only by ASCII case (A vs a) 482 o the specific sequence of 3 characters NIL 484 A good solution to these issues is to prefix every ID with a single 485 alphabetical character. 487 8.2. Interaction with special cases 489 The case of RENAME INBOX may need special handling, as it has special 490 behaviour as defined in [RFC3501] section 6.3.5. 492 It is advisable (though not required) to have MAILBOXID be globally 493 unique, but it is only required to be unique within messages offered 494 to a single client login to a single server hostname. For example, a 495 proxy which aggregates multiple independent servers MUST NOT 496 advertise the OBJECTID capability unless it can guarantee that 497 different objects will never use the same identifiers, even if 498 backend object collide. 500 8.3. Client usage 502 Servers that implement both RFC 6154 and this specification should 503 optimize their execution of command like UID SEARCH OR EMAILID 1234 504 EMAILID 4321. 506 Clients can assume that searching the all-mail mailbox using OR/ 507 EMAILID or OR/THREADID is a fast way to find messages again if some 508 other client has moved them out of the mailbox where they were 509 previously seen. 511 Clients that cache data offline should fetch the EMAILID of all new 512 messages to avoid re-downloading already cached message details. 514 Clients should fetch the MAILBOXID for any new mailboxes before 515 discarding cache data for any mailbox which is no longer present on 516 the server, so that they can detect renames and avoid re-downloading 517 data. 519 9. Future considerations 521 This extension is intentionally defined to be compatible with the 522 data model in [I-D.ietf-jmap-mail]. 524 A future extension could be proposed to give a way to SELECT a 525 mailbox by MAILBOXID rather than name. 527 A future extension to [RFC5228] could allow fileinto by MAILBOXID 528 rather than name. 530 An extension to allow fetching message content directly via EMAILID 531 and message listings by THREADID could be proposed. 533 10. IANA Considerations 535 IANA is requested to add "OBJECTID" to the "IMAP Capabilities" 536 registry located at with a Reference of [[THIS RFC]]. 539 IANA is requested to add "MAILBOXID" to the "IMAP Response Codes" 540 registry located at with a Reference of [[THIS RFC]]. 543 11. Security Considerations 545 It is strongly advised that servers generate OBJECTIDs which are safe 546 to use as filesystem names, and unlikely to be auto-detected as 547 numbers. See implementation considerations. 549 If a digest is used for ID generation, it must have a collision 550 resistent property, so server implementations are advised to monitor 551 current security research and choose secure digests. As the IDs are 552 generated by the server, it will be possible to migrate to a new hash 553 by just using the new algorith when creating new IDs. This is 554 particularly true if a prefix is used on each ID, which can be 555 changed when the algorithm changes. 557 The use of a digest for ID generation may be used as proof that a 558 particular sequence of bytes was seen by the server, however this is 559 only a risk if IDs are leaked to clients who don't have permission to 560 fetch the data directly. Servers that are expected to handle highly 561 sensitive data should consider using a ID generation mechanism which 562 doesn't derive from a digest. 564 See also the security considerations in [RFC3501] section 11. 566 12. Changes 568 To be removed by the editor before publication 570 12.1. draft-ietf-extra-imap-objectid-07 572 o updated boilerplate to RFC8174 (Benjamin Kaduk review) 574 o fixed spelling of invariants (Benjamin Kaduk review) 576 o block quoted ABNF for better text formatting (Benjamin Kaduk 577 review) 579 o clarified that servers can just switch to a new digest without 580 changing old IDs (Benjamin Kaduk review) 582 o changed use of folder to mailbox to avoid confusion (Warren Kumari 583 review) 585 o made both IANA requests say "reference of this RFC" (Warren Kumari 586 review) 588 12.2. draft-ietf-extra-imap-objectid-06 590 o fixed one more missing space in ABNF (ad review) 592 o made one more MUST for mailbox being retained on rename (genart 593 review) 595 o updated ABNF to also extend msg-att-static (validator review) 597 o lowercased NIL => nil in ABNF (validator review) 599 12.3. draft-ietf-extra-imap-objectid-05 601 o changed some SHOULD to lower case in advice sections (genart 602 review) 604 o clarified that THREADID MUST NOT change 606 12.4. draft-ietf-extra-imap-objectid-04 608 o described NIL THREADID in more detail (ad review) 610 o made RFC5256 a normative reference (ad review) 612 o fixed ABNF missing quote (ad review) 613 o documented hash upgrade process (ad review) 615 o referenced RFC3501 for INBOX rename (ad review) 617 o referenced RFC3501 security considerations (secdir review) 619 o turned mealy-mouthed "SHOULDs" in to "MUSTs" on immutability 620 (genart review) 622 o remove suggested algorithms which are no longer legitimate (genart 623 review) 625 o updated proxy advice to suggest rewriting ids (genart review) 627 o fixed minor gramatical issues (genart review) 629 o required that EMAILID and THREADID are not identical (own 630 decision) 632 12.5. draft-ietf-extra-imap-objectid-03 634 o added RFC3501 to Abstract 636 o updated [[THIS RFC]] to not fail idnits 638 o changed jmap-mail to be informative rather than normative 640 o shortened IDs to stop wrapping and outdents in IMAP examples 642 12.6. draft-ietf-extra-imap-objectid-02 644 o added "Client usage" section 646 12.7. draft-ietf-extra-imap-objectid-01 648 o added "updates" for RFC3501 650 o fixed domains in thread example 652 o described threading in more detail 654 o added IANA request for Response Code 656 o clarified RFC2119 references 658 o simplified some waffle in wording 660 o added security consideration to choose good digest 661 o added MAILBOXID-UID suggestion for EMAILID generation 663 o updated ABNF normative reference to RFC5234 665 12.8. draft-ietf-extra-imap-objectid-00 667 o renamed draft to be objectid rather than uniqueid 669 o renamed UNIQUEID (capability) to OBJECTID 671 o restricted objectid to 64 safe characters 673 o added security considerations and advice about choosing objectid 675 o wrapped all responses in () for RFC4466 compatibility 677 o signifiant rewrite of all sections 679 12.9. draft-ietf-extra-imap-uniqueid-00 681 o renamed draft to be an EXTRA document 683 o added example for LIST RETURN STATUS 685 o started work on ABNF 687 o attempted to add response codes for EMAILID and THREADID 689 12.10. draft-gondwana-imap-uniqueid-01 691 o renamed UNIQUEID (status item) to MAILBOXID 693 o renamed MSGID to EMAILID 695 o renamed THRID to THREADID 697 o added TODO section 699 12.11. draft-gondwana-imap-uniqueid-00 701 o initial upload with names UNIQUEID/MSGID/THRID 703 13. Acknowledgments 705 The EXTRA working group at IETF. In particular feedback from Arnt 706 Gulbrandsen, Brandon Long, Chris Newman and Josef Sipek. 708 The Gmail X-GM-THRID and X-GM-MSGID implementation as currently 709 defined at . 712 Dovecot X-GUID implementation. 714 13.1. Appendix 1: ideas for implementing object identifiers 716 Ideas for calculating MAILBOXID: 718 o [RFC4122] UUID 720 o Server assigned sequence number (guaranteed not to be reused) 722 Ideas for implementing EMAILID: 724 o Digest of message content (RFC822 bytes) - expensive unless cached 726 o [RFC4122] UUID 728 o Server assigned sequence number (guaranteed not to be reused) 730 Ideas for implementing THREADID: 732 o Derive from EMAILID of first seen message in the thread. 734 o [RFC4122] UUID 736 o Server assigned sequence number (guaranteed not to be reused) 738 There is a need to index and look up reference/in-reply-to data at 739 message creation to efficiently find matching messages for threading. 740 Threading may be either across mailboxes, or within each mailbox 741 only. The server has significant leeway here. 743 14. References 745 14.1. Normative References 747 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 748 Requirement Levels", BCP 14, RFC 2119, 749 DOI 10.17487/RFC2119, March 1997, 750 . 752 [RFC3501] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION 753 4rev1", RFC 3501, DOI 10.17487/RFC3501, March 2003, 754 . 756 [RFC4315] Crispin, M., "Internet Message Access Protocol (IMAP) - 757 UIDPLUS extension", RFC 4315, DOI 10.17487/RFC4315, 758 December 2005, . 760 [RFC4466] Melnikov, A. and C. Daboo, "Collected Extensions to IMAP4 761 ABNF", RFC 4466, DOI 10.17487/RFC4466, April 2006, 762 . 764 [RFC5228] Guenther, P., Ed. and T. Showalter, Ed., "Sieve: An Email 765 Filtering Language", RFC 5228, DOI 10.17487/RFC5228, 766 January 2008, . 768 [RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax 769 Specifications: ABNF", STD 68, RFC 5234, 770 DOI 10.17487/RFC5234, January 2008, 771 . 773 [RFC5256] Crispin, M. and K. Murchison, "Internet Message Access 774 Protocol - SORT and THREAD Extensions", RFC 5256, 775 DOI 10.17487/RFC5256, June 2008, 776 . 778 [RFC5819] Melnikov, A. and T. Sirainen, "IMAP4 Extension for 779 Returning STATUS Information in Extended LIST", RFC 5819, 780 DOI 10.17487/RFC5819, March 2010, 781 . 783 [RFC6851] Gulbrandsen, A. and N. Freed, Ed., "Internet Message 784 Access Protocol (IMAP) - MOVE Extension", RFC 6851, 785 DOI 10.17487/RFC6851, January 2013, 786 . 788 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 789 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 790 May 2017, . 792 14.2. Informative References 794 [I-D.ietf-jmap-mail] 795 Jenkins, N., "JMAP for Mail", draft-ietf-jmap-mail-06 796 (work in progress), July 2018. 798 [RFC4122] Leach, P., Mealling, M., and R. Salz, "A Universally 799 Unique IDentifier (UUID) URN Namespace", RFC 4122, 800 DOI 10.17487/RFC4122, July 2005, 801 . 803 Author's Address 805 Bron Gondwana (editor) 806 FastMail 807 Level 2, 114 William St 808 Melbourne VIC 3000 809 Australia 811 Email: brong@fastmailteam.com 812 URI: https://www.fastmail.com