EXTRA B. Gondwana, Ed. Internet-Draft FastMail Updates: 5228 (if approved) 17 June 2020 Intended status: Standards Track Expires: 19 December 2020 Sieve Email Filtering: delivery by mailboxid draft-gondwana-sieve-mailboxid-02 Abstract The OBJECTID capability of the IMAP protocol (I-D.ietf-extra-imap- objectid) allows clients to identify mailboxes by a unique identifier which survives rename. In contrast, the Sieve mail filtering language (RFC 5228) currently has no such capability. This memo defines a Sieve extension that fills this gap: it adds a method for specifying the unique identifier of a mailbox as a target for fileinto rules, and a method for testing the existence of a mailbox by its unique identifier. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. 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." This Internet-Draft will expire on 19 December 2020. Copyright Notice Copyright (c) 2020 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/ license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components Gondwana Expires 19 December 2020 [Page 1] Internet-Draft Sieve MAILBOXID June 2020 extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Conventions Used In This Document . . . . . . . . . . . . . . 2 3. Sieve capability string . . . . . . . . . . . . . . . . . . . 3 4. Argument ":mailboxid" to Command "fileinto" . . . . . . . . . 3 4.1. Interaction with "mailbox" extension . . . . . . . . . . 3 4.2. Interaction with "specialuse" extension . . . . . . . . . 4 4.3. Interaction with "fcc" extension . . . . . . . . . . . . 5 5. Test ":mailboxidexists" . . . . . . . . . . . . . . . . . . . 5 6. Formal Syntax . . . . . . . . . . . . . . . . . . . . . . . . 6 7. Security considerations . . . . . . . . . . . . . . . . . . . 6 8. IANA considerations . . . . . . . . . . . . . . . . . . . . . 6 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7 10. Changes . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 10.1. draft-gondwana-sieve-mailboxid-02 . . . . . . . . . . . 7 10.2. draft-gondwana-sieve-mailboxid-01 . . . . . . . . . . . 7 10.3. draft-gondwana-sieve-mailboxid-00 . . . . . . . . . . . 7 11. TODO . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 12. Normative References . . . . . . . . . . . . . . . . . . . . 8 13. Informative References . . . . . . . . . . . . . . . . . . . 8 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 9 1. Introduction Sieve rules are sometimes created using graphical interfaces which allow users to select the mailbox to be used as a target for a rule. If that mailbox is renamed, the client may also update its internal representation of the rule and update the sieve script to match, however this is a multi-step process and subject to partial failures. Also, if the folder is renamed by a different mechanism (e.g. another IMAP client) the rules will get out of sync. By extending "fileinto" to reference an immutable mailboxid, sieve rules can continue to target the same mailbox, regardless of how it gets renamed. 2. Conventions Used In This Document The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here. Gondwana Expires 19 December 2020 [Page 2] Internet-Draft Sieve MAILBOXID June 2020 3. Sieve capability string The server advertises the capability "mailboxid", and scripts which use the following extensions MUST explicitly request the capability "mailboxid". Example: require "mailboxid"; 4. Argument ":mailboxid" to Command "fileinto" Normally, the "fileinto" command delivers the message in the mailbox specified using its positional mailbox argument. However, if the optional ":mailboxid" argument is also specified, the "fileinto" command first checks whether a mailbox exists in the user's personal namespace [RFC2342] with the specified [I-D.ietf-extra-imap-objectid] MAILBOXID. If that is the case, that mailbox is used for delivery instead. If there is no such mailbox, the "fileinto" action proceeds as it would without the ":mailboxid" argument. The tagged argument ":mailboxid" to fileinto consumes one additional token, a string with the objectid of the mailbox to file into. Example: require "fileinto"; require "mailboxid"; if header :contains ["from"] "coyote" { fileinto :mailboxid "F6352ae03-b7f5-463c-896f-d8b48ee3" "INBOX.harassment"; } 4.1. Interaction with "mailbox" extension For servers which also support the [RFC5490] mailbox extension, the ":create" modifier to fileinto does not create mailbox with the specified mailboxid, however it may be specified and interacts as normal with all other extensions. Example: Gondwana Expires 19 December 2020 [Page 3] Internet-Draft Sieve MAILBOXID June 2020 require "fileinto"; require "mailboxid"; require "mailbox"; fileinto :mailboxid "Fnosuch" :create "INBOX.no-such-folder"; # creates INBOX.no-such-folder, but it doesn't # get the "Fnosuch" mailboxid. 4.2. Interaction with "specialuse" extension For servers which also support [I-D.ietf-extra-sieve-special-use], if a fileinto command has both ":mailboxid" and ":special-use" specified, then the mailboxid is resolved first. If the mailboxid does not exist, then the special-use is evaluated next following the process specified in [I-D.ietf-extra-sieve-special-use] - this includes processing of [RFC5490] ":create" tags to add the special- use on creation. Example: require "fileinto"; require "mailboxid"; require "special-use"; if header :contains ["from"] "coyote" { fileinto :mailboxid "F6352ae03-b7f5-463c-896f-d8b48ee3" :specialuse "\\Junk" "INBOX.harassment"; } Example: require "fileinto"; require "mailboxid"; require "mailbox"; require "special-use"; fileinto :mailboxid "F1234567" :specialuse "\\Archive" :create "INBOX.Archive"; # creates INBOX.Archive with use \Archive but # with a different mailboxid. Gondwana Expires 19 December 2020 [Page 4] Internet-Draft Sieve MAILBOXID June 2020 4.3. Interaction with "fcc" extension This document extends the definition of the :fcc argument so that it can optionally be used with the ":mailboxid" argument. FCC =/ [":mailboxid" ] If the optional ":mailboxid" argument is specified with ":fcc", it instructs the Sieve interpreter to check whether a mailbox exists with the specific mailboxid. If such a mailbox exists, the generated message is filed into that mailbox. Otherwise, the generated message is filed into the ":fcc" target mailbox. Example: require ["enotify", "fcc", "mailboxid"]; notify :fcc "INBOX.Sent" :mailboxid "F6352ae03-b7f5-463c-896f-d8b48ee3" :message "You got mail!" "mailto:ken@example.com"; 5. Test ":mailboxidexists" The "mailboxidexists" test is true if all mailboxes listed in the "mailboxids" argument exist in the mailstore, and each allows the user in whose context the Sieve script runs to "deliver" messages into it. When the mailstore is an IMAP server, "delivery" of messages is possible if: a) the READ-WRITE response code is present for the mailbox (see Section 7.1 of [RFC3501]), if IMAP Access Control List (ACL) [RFC4314] is not supported by the server, or b) the user has 'p' or 'i' rights for the mailbox (see Section 5.2 of [RFC4314]). Note that a successful "mailboxidexists" test for a mailbox doesn't necessarily mean that a "fileinto :mailboxid" action on this mailbox would succeed. For example, the "fileinto" action might put user over quota. The "mailboxidexists" only verifies existence of the mailbox and whether the user in whose context the Sieve script runs has permissions to execute "fileinto" on it. Example: Gondwana Expires 19 December 2020 [Page 5] Internet-Draft Sieve MAILBOXID June 2020 require "fileinto"; require "mailboxid"; if header :contains ["from"] "coyote" { if mailboxidexists "F6352ae03-b7f5-463c-896f-d8b48ee3" { fileinto :mailboxid "F6352ae03-b7f5-463c-896f-d8b48ee3" "INBOX.harassment"; } else { fileinto "INBOX.harassment"; } } Not to implementers: this test behaves identically to the "mailboxexists" test defined in [RFC5490] but operates on mailboxids rather than mailbox names. 6. Formal Syntax test /= ":mailboxidexists" string-list tag /= ":mailboxid" string If [I-D.ietf-extra-sieve-fcc] is supported: FCC =/ [":mailboxid" ] 7. Security considerations Because mailboxid is always generated by the server, implementations MUST NOT allow sieve to make an endrun around this protection by creating mailboxes with the specified ID by using ":create" and ":mailboxid" in a fileinto rule for a non-existant mailbox. Implementers are referred to the security considerations sections of those documents in [RFC5228], [I-D.ietf-extra-imap-objectid]. 8. IANA considerations IANA are requested to add a capability to the sieve-extensions registry: Gondwana Expires 19 December 2020 [Page 6] Internet-Draft Sieve MAILBOXID June 2020 To: iana@iana.org Subject: Registration of new Sieve extension Capability name: mailboxid Description: adds test for checking for mailbox existence by objectid and a new optional argument to fileinto to select the destination mailbox using objectid. RFC number: this RFC Contact address: The EXTRA discussion list 9. Acknowledgements This document borrows heavily from [RFC5490] for the matching mailboxexists test, and from [I-D.ietf-extra-sieve-special-use] for an example of modifying the fileinto command. Thanks to Ned Freed and Ken Murchison for feedback on the EXTRA mailing list. 10. Changes (EDITOR: remove this section before publication) 10.1. draft-gondwana-sieve-mailboxid-02 * Update document date by a couple of years! Ooops, it got forgotten after a WGLC which got not dissent. * Create xml2rfc v3 output. 10.2. draft-gondwana-sieve-mailboxid-01 * Switch to :mailboxid tagged parameter value with fallback mailbox name. * Document interaction with "mailbox". * Document interaction with "special-use". * Document interaction with "fcc". * Document security considerations around :mailboxid and :create. 10.3. draft-gondwana-sieve-mailboxid-00 * Initial version. Gondwana Expires 19 December 2020 [Page 7] Internet-Draft Sieve MAILBOXID June 2020 11. TODO Is there a more explicit way to update the grammar? It seems less fully specified than IMAP. 12. Normative References [RFC5228] Guenther, P., Ed. and T. Showalter, Ed., "Sieve: An Email Filtering Language", RFC 5228, DOI 10.17487/RFC5228, January 2008, . [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC2342] Gahrns, M. and C. Newman, "IMAP4 Namespace", RFC 2342, DOI 10.17487/RFC2342, May 1998, . [I-D.ietf-extra-imap-objectid] Gondwana, B., "IMAP Extension for object identifiers", Work in Progress, Internet-Draft, draft-ietf-extra-imap- objectid-08, 2 August 2018, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . 13. Informative References [I-D.ietf-extra-sieve-special-use] Bosch, S., "Sieve Email Filtering: Delivering to Special- Use Mailboxes", Work in Progress, Internet-Draft, draft- ietf-extra-sieve-special-use-05, 24 January 2019, . [RFC3501] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION 4rev1", RFC 3501, DOI 10.17487/RFC3501, March 2003, . [RFC4314] Melnikov, A., "IMAP4 Access Control List (ACL) Extension", RFC 4314, DOI 10.17487/RFC4314, December 2005, . Gondwana Expires 19 December 2020 [Page 8] Internet-Draft Sieve MAILBOXID June 2020 [RFC5490] Melnikov, A., "The Sieve Mail-Filtering Language -- Extensions for Checking Mailbox Status and Accessing Mailbox Metadata", RFC 5490, DOI 10.17487/RFC5490, March 2009, . [I-D.ietf-extra-sieve-fcc] Murchison, K. and B. Gondwana, "Sieve Extension: File Carbon Copy (Fcc)", Work in Progress, Internet-Draft, draft-ietf-extra-sieve-fcc-09, 13 January 2019, . Author's Address Bron Gondwana (editor) FastMail Level 2, 114 William St Melbourne VIC 3000 Australia Email: brong@fastmailteam.com URI: https://www.fastmail.com Gondwana Expires 19 December 2020 [Page 9]