< draft-ietf-extra-sieve-special-use-01.txt		draft-ietf-extra-sieve-special-use-02.txt >
	EXTRA S. Bosch		EXTRA S. Bosch
	Internet-Draft Dovecot Oy		Internet-Draft Dovecot Oy
	Intended status: Standards Track January 7, 2018		Intended status: Standards Track March 5, 2018
	Expires: July 11, 2018		Expires: September 6, 2018
	Sieve Email Filtering: Delivering to Special-Use Mailboxes		Sieve Email Filtering: Delivering to Special-Use Mailboxes
	draft-ietf-extra-sieve-special-use-01		draft-ietf-extra-sieve-special-use-02
	Abstract		Abstract
	The SPECIAL-USE capability of the IMAP protocol (RFC 6154) allows		The SPECIAL-USE capability of the IMAP protocol (RFC 6154) allows
	clients to identify special-use mailboxes; e.g., where draft or sent		clients to identify special-use mailboxes; e.g., where draft or sent
	messages should be put. This simplifies client configuration. In		messages should be put. This simplifies client configuration. In
	contrast, the Sieve mail filtering language (RFC 5228) currently has		contrast, the Sieve mail filtering language (RFC 5228) currently has
	no such capability. This memo defines a Sieve extension that fills		no such capability. This memo defines a Sieve extension that fills
	this gap: it adds a test for checking whether a special-use attribute		this gap: it adds a test for checking whether a special-use attribute
	is assigned for a particular mailbox or any mailbox, and it adds the		is assigned for a particular mailbox or any mailbox, and it adds the
	skipping to change at page 1, line 38 ¶		skipping to change at page 1, line 38 ¶
	Internet-Drafts are working documents of the Internet Engineering		Internet-Drafts are working documents of the Internet Engineering
	Task Force (IETF). Note that other groups may also distribute		Task Force (IETF). Note that other groups may also distribute
	working documents as Internet-Drafts. The list of current Internet-		working documents as Internet-Drafts. The list of current Internet-
	Drafts is at http://datatracker.ietf.org/drafts/current/.		Drafts is at http://datatracker.ietf.org/drafts/current/.
	Internet-Drafts are draft documents valid for a maximum of six months		Internet-Drafts are draft documents valid for a maximum of six months
	and may be updated, replaced, or obsoleted by other documents at any		and may be updated, replaced, or obsoleted by other documents at any
	time. It is inappropriate to use Internet-Drafts as reference		time. It is inappropriate to use Internet-Drafts as reference
	material or to cite them other than as "work in progress."		material or to cite them other than as "work in progress."
	This Internet-Draft will expire on July 11, 2018.		This Internet-Draft will expire on September 6, 2018.
	Copyright Notice		Copyright Notice
	Copyright (c) 2018 IETF Trust and the persons identified as the		Copyright (c) 2018 IETF Trust and the persons identified as the
	document authors. All rights reserved.		document authors. All rights reserved.
	This document is subject to BCP 78 and the IETF Trust's Legal		This document is subject to BCP 78 and the IETF Trust's Legal
	Provisions Relating to IETF Documents		Provisions Relating to IETF Documents
	(http://trustee.ietf.org/license-info) in effect on the date of		(http://trustee.ietf.org/license-info) in effect on the date of
	publication of this document. Please review these documents		publication of this document. Please review these documents
	skipping to change at page 2, line 19 ¶		skipping to change at page 2, line 19 ¶
	Table of Contents		Table of Contents
	1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2		1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
	2. Conventions Used in This Document . . . . . . . . . . . . . . 3		2. Conventions Used in This Document . . . . . . . . . . . . . . 3
	3. Test "specialuse_exists" . . . . . . . . . . . . . . . . . . 3		3. Test "specialuse_exists" . . . . . . . . . . . . . . . . . . 3
	4. ":specialuse" Argument to "fileinto" Command . . . . . . . . 4		4. ":specialuse" Argument to "fileinto" Command . . . . . . . . 4
	4.1. Interaction with ":create" Argument to "fileinto" Command 5		4.1. Interaction with ":create" Argument to "fileinto" Command 5
	5. Sieve Capability Strings . . . . . . . . . . . . . . . . . . 5		5. Sieve Capability Strings . . . . . . . . . . . . . . . . . . 5
	6. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 5		6. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 5
	7. Security Considerations . . . . . . . . . . . . . . . . . . . 6		7. Security Considerations . . . . . . . . . . . . . . . . . . . 6
	8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6		8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
	9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7		9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7
	10. References . . . . . . . . . . . . . . . . . . . . . . . . . 7		10. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
	10.1. Normative References . . . . . . . . . . . . . . . . . . 7		10.1. Normative References . . . . . . . . . . . . . . . . . . 7
	10.2. Informative References . . . . . . . . . . . . . . . . . 8		10.2. Informative References . . . . . . . . . . . . . . . . . 8
	Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 8		Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 8
	1. Introduction		1. Introduction
	Commonly, several mailboxes in an IMAP message store [IMAP] have a		Commonly, several mailboxes in an IMAP message store [IMAP] have a
	special use; e.g. it is where the user's draft messages are stored,		special use; e.g. it is where the user's draft messages are stored,
	skipping to change at page 3, line 9 ¶		skipping to change at page 3, line 9 ¶
	testing for the presence of a special-use attribute in the "/private/		testing for the presence of a special-use attribute in the "/private/
	specialuse" IMAP METADATA [IMAP-METADATA] entry of a mailbox. Still,		specialuse" IMAP METADATA [IMAP-METADATA] entry of a mailbox. Still,
	not all implementers will be willing to add the complexity of the		not all implementers will be willing to add the complexity of the
	IMAP METADATA capability, just to provide access to special-use		IMAP METADATA capability, just to provide access to special-use
	attributes to the Sieve interpreter.		attributes to the Sieve interpreter.
	This document defines an extension to the Sieve mail filtering		This document defines an extension to the Sieve mail filtering
	language that adds the ability to freely access mailbox special-use		language that adds the ability to freely access mailbox special-use
	attributes. It adds a test called "specialuse_exists" that checks		attributes. It adds a test called "specialuse_exists" that checks
	whether a special-use attribute is assigned for a particular mailbox		whether a special-use attribute is assigned for a particular mailbox
	or - if omitted - any mailbox. It also adds the ability to file		or - if omitted - any of the user's personal mailboxes. It also adds
	messages into an anonymous mailbox that has a particular special-use		the ability to file messages into an anonymous personal mailbox that
	attribute assigned using a ":specialuse" argument for the "fileinto"		has a particular special-use attribute assigned using a ":specialuse"
	command [SIEVE].		argument for the "fileinto" command [SIEVE].
	2. Conventions Used in This Document		2. Conventions Used in This Document
	The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",		The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
	"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this		"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
	document are to be interpreted as described in [KEYWORDS].		document are to be interpreted as described in [KEYWORDS].
	Conventions for notations are as in [SIEVE] Section 1.1, including		Conventions for notations are as in [SIEVE] Section 1.1, including
	use of the "Usage:" label for the definition of action and tagged		use of the "Usage:" label for the definition of action and tagged
	arguments syntax.		arguments syntax.
	3. Test "specialuse_exists"		3. Test "specialuse_exists"
	Usage: specialuse_exists [<mailbox: string>]		Usage: specialuse_exists [<mailbox: string>]
	<special-use-flags: string-list>		<special-use-flags: string-list>
	If the "mailbox" string argument is omitted, the "specialuse_exists"		If the "mailbox" string argument is omitted, the "specialuse_exists"
	test yields true if all of the following statements are true for each		test yields true if all of the following statements are true for each
	of the special-use flags listed in the "special-use-flags" argument:		of the special-use flags listed in the "special-use-flags" argument:
	a. at least one mailbox exists in the mail store that has that		a. at least one mailbox exists in the user's personal namespace
	particular special-use flag assigned, and		[NAMESPACE] that has that particular special-use flag assigned,
			and
	b. that mailbox allows the user in whose context the Sieve script		b. that mailbox allows the user in whose context the Sieve script
	runs to "deliver" messages into it.		runs to "deliver" messages into it.
	If the "mailbox" argument is specified, the "specialuse_exists" test		If the "mailbox" argument is specified, the "specialuse_exists" test
	yields true if all of the following statements are true:		yields true if all of the following statements are true:
	a. the indicated mailbox exists,		a. the indicated mailbox exists,
	b. that mailbox allows the user in whose context the Sieve script		b. that mailbox allows the user in whose context the Sieve script
	skipping to change at page 4, line 13 ¶		skipping to change at page 4, line 17 ¶
	messages into a mailbox is deemed possible.		messages into a mailbox is deemed possible.
	4. ":specialuse" Argument to "fileinto" Command		4. ":specialuse" Argument to "fileinto" Command
	Usage: fileinto [:specialuse <special-use-flag: string>]		Usage: fileinto [:specialuse <special-use-flag: string>]
	<mailbox: string>		<mailbox: string>
	Normally, the "fileinto" command delivers the message in the mailbox		Normally, the "fileinto" command delivers the message in the mailbox
	specified using its positional mailbox argument. However, if the		specified using its positional mailbox argument. However, if the
	optional ":specialuse" argument is also specified, the "fileinto"		optional ":specialuse" argument is also specified, the "fileinto"
	command first checks whether a mailbox exists with the specified		command first checks whether a mailbox exists in the user's personal
	special-use flag assigned to it. If that is the case, that special-		namespace [NAMESPACE] with the specified special-use flag assigned to
	use mailbox is used for delivery instead. If there is no such		it. If that is the case, that special-use mailbox is used for
	mailbox or if the specified special-use flag is unknown to the		delivery instead. If there is no such mailbox or if the specified
	implementation in general, the "fileinto" action proceeds as it would		special-use flag is unknown to the implementation in general, the
	without the ":specialuse" argument.		"fileinto" action proceeds as it would without the ":specialuse"
			argument.
	Summarizing, if the ":specialuse" argument is specified, the fileinto		Summarizing, if the ":specialuse" argument is specified, the fileinto
	command deals with two mailboxes that may or may not exist:		command deals with two mailboxes that may or may not exist:
	o An anonymous special-use mailbox, which has at least the special-		o An anonymous special-use mailbox in the user's personal namespace,
	use flag specified with the ":specialuse" argument assigned to it.		which has at least the special-use flag specified with the
			":specialuse" argument assigned to it.
	o The default mailbox named by the positional string argument of the		o The default mailbox named by the positional string argument of the
	"fileinto" command, which is used when the special-use mailbox is		"fileinto" command, which is used when the special-use mailbox is
	not found.		not found.
	The special-use flag specified with the ":specialuse" argument MUST		The special-use flag specified with the ":specialuse" argument MUST
	conform to the "use-attr" syntax described in Section 6 of RFC6154		conform to the "use-attr" syntax described in Section 6 of RFC6154
	[SIEVE-MAILBOX]. Implementations SHOULD handle an invalid special-		[SIEVE-MAILBOX]. Implementations SHOULD handle an invalid special-
	use flag in the same way as an invalid mailbox name is handled. The		use flag in the same way as an invalid mailbox name is handled. The
	string parameter of the ":specialuse" argument is not a constant		string parameter of the ":specialuse" argument is not a constant
	string, which means that variable substitutions are allowed when the		string, which means that variable substitutions are allowed when the
	"variables" extension [VARIABLES] is active. In that case, the		"variables" extension [VARIABLES] is active. In that case, the
	syntax of the special-use flag is only verified at runtime.		syntax of the special-use flag is only verified at runtime.
	If neither the special-use mailbox nor the default mailbox exists,		If neither the special-use mailbox nor the default mailbox exists,
	the "fileinto" action MUST proceed exactly as it does in case the		the "fileinto" action MUST proceed exactly as it does in case the
	":specialuse" is argument is absent and the mailbox named by its		":specialuse" is argument is absent and the mailbox named by its
	positional argument does not exist. The various options for handling		positional argument does not exist. The various options for handling
	this situation are described in Section 4.1 of RFC5228 [SIEVE].		this situation are described in Section 4.1 of RFC5228 [SIEVE].
	More than one mailbox can have a particular special-use flag		More than one mailbox in the user's personal namespace can have a
	assigned. In that case, the mailbox that is chosen for delivery is		particular special-use flag assigned. In case of such ambiguity, the
	implementation-defined. However, implementations MUST ensure that		mailbox that is chosen for delivery is implementation-defined.
	this choice is made consistently, so that the same mailbox is used		However, while the set of mailboxes to which the involved special-use
	every time.		flags are assigned remains unchanged, implementations MUST ensure
			that the mailbox choice is made consistently, so that the same
			mailbox is used every time. Conversely, the chosen mailbox MAY
			change once the special-use flag assignments that are relevant for
			the mailbox choice are changed (usually by user interaction).
	If delivery to the special-use mailbox fails for reasons not relating		If delivery to the special-use mailbox fails for reasons not relating
	to its existence, the Sieve interpreter MUST NOT subsequently attempt		to its existence, the Sieve interpreter MUST NOT subsequently attempt
	delivery in the indicated default mailbox as a fall-back. Instead,		delivery in the indicated default mailbox as a fall-back. Instead,
	it MUST proceed exactly as it does in case the ":specialuse" argument		it MUST proceed exactly as it does in case the ":specialuse" argument
	is absent and delivery to the mailbox named by its positional		is absent and delivery to the mailbox named by its positional
	argument fails. This prevents the situation where messages are		argument fails. This prevents the situation where messages are
	unexpectedly spread over two mailboxes in case transient or		unexpectedly spread over two mailboxes in case transient or
	intermittent delivery failures occur.		intermittent delivery failures occur.
	skipping to change at page 6, line 40 ¶		skipping to change at page 6, line 49 ¶
	specialuse_exists "${mailbox}" "\\Junk") {		specialuse_exists "${mailbox}" "\\Junk") {
	redirect "spam-report@example.org";		redirect "spam-report@example.org";
	}		}
	7. Security Considerations		7. Security Considerations
	Security considerations are discussed in [SIEVE], [VARIABLES], and		Security considerations are discussed in [SIEVE], [VARIABLES], and
	[SPECIAL-USE]. It is believed that this extension does not introduce		[SPECIAL-USE]. It is believed that this extension does not introduce
	any additional security concerns.		any additional security concerns.
			Note that this specification explicitly restricts the anonymous
			special-use mailbox to the user's personal namespace. First, this
			avoids the need to search the entire mail storage for mailboxes that
			have a particular special-use flag assigned. This could put undue
			load on the system, while shared special-use mailboxes are deemed of
			limited use with the currently defined special-use flags. Secondly,
			it prevents security concerns with shared mailboxes that have
			special-use flags assigned that apply to all users. Searching the
			entire mail storage for special-use mailboxes could lead to messages
			unexpectedly or even maliciously being filed to shared mailboxes.
			This restriction could be lifted for particular future special-use
			flags, but such new flags should have a clear application for shared
			mailboxes and the security concerns should be considered carefully.
	8. IANA Considerations		8. IANA Considerations
	The following template specifies the IANA registration of the Sieve		The following template specifies the IANA registration of the Sieve
	extension specified in this document:		extension specified in this document:
	To: iana@iana.org		To: iana@iana.org
	Subject: Registration of new Sieve extension		Subject: Registration of new Sieve extension
	Capability name: special-use		Capability name: special-use
	Description: adds a test for checking whether an IMAP		Description: adds a test for checking whether an IMAP
	skipping to change at page 7, line 42 ¶		skipping to change at page 8, line 9 ¶
	[IMAP-METADATA]		[IMAP-METADATA]
	Daboo, C., "The IMAP METADATA Extension", RFC 5464,		Daboo, C., "The IMAP METADATA Extension", RFC 5464,
	DOI 10.17487/RFC5464, February 2009,		DOI 10.17487/RFC5464, February 2009,
	<http://www.rfc-editor.org/info/rfc5464>.		<http://www.rfc-editor.org/info/rfc5464>.
	[KEYWORDS]		[KEYWORDS]
	Bradner, S., "Key words for use in RFCs to Indicate		Bradner, S., "Key words for use in RFCs to Indicate
	Requirement Levels", BCP 14, RFC 2119, March 1997.		Requirement Levels", BCP 14, RFC 2119, March 1997.
			[NAMESPACE]
			Gahrns, M. and C. Newman, "IMAP4 Namespace", RFC 2342,
			DOI 10.17487/RFC2342, May 1998, <https://www.rfc-
			editor.org/info/rfc2342>.
	[SIEVE] Guenther, P. and T. Showalter, "Sieve: An Email Filtering		[SIEVE] Guenther, P. and T. Showalter, "Sieve: An Email Filtering
	Language", RFC 5228, January 2008.		Language", RFC 5228, January 2008.
	[SIEVE-MAILBOX]		[SIEVE-MAILBOX]
	Melnikov, A., "The Sieve Mail-Filtering Language --		Melnikov, A., "The Sieve Mail-Filtering Language --
	Extensions for Checking Mailbox Status and Accessing		Extensions for Checking Mailbox Status and Accessing
	Mailbox Metadata", RFC 5490, March 2009.		Mailbox Metadata", RFC 5490, March 2009.
	[SPECIAL-USE]		[SPECIAL-USE]
	Leiba, B. and J. Nicolson, "IMAP LIST Extension for		Leiba, B. and J. Nicolson, "IMAP LIST Extension for
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