rfc9738v1.txt		rfc9738.txt
	skipping to change at line 15 ¶		skipping to change at line 15 ¶
	ISSN: 2070-1721 V. Nagulakonda		ISSN: 2070-1721 V. Nagulakonda
	Yahoo!		Yahoo!
	L. Alves		L. Alves
	February 2025		February 2025
	IMAP MESSAGELIMIT Extension		IMAP MESSAGELIMIT Extension
	Abstract		Abstract
	The MESSAGELIMIT extension of the Internet Message Access Protocol		The MESSAGELIMIT extension of the Internet Message Access Protocol
	(RFC 3501/RFC 9051) allows servers to announce a limit on the number		(RFCs 3501 and 9051) allows servers to announce a limit on the number
	of messages that can be processed in a single FETCH, SEARCH, STORE,		of messages that can be processed in a single FETCH, SEARCH, STORE,
	COPY, or MOVE command (or their UID variants), or in a single APPEND		COPY, or MOVE command (or their UID variants), or in a single APPEND
	or UID EXPUNGE command. This helps servers to control resource usage		or UID EXPUNGE command. This helps servers to control resource usage
	when performing various IMAP operations. This helps clients to know		when performing various IMAP operations. This helps clients to know
	the message limit enforced by the corresponding IMAP server and avoid		the message limit enforced by the corresponding IMAP server and avoid
	issuing commands that would exceed such limit.		issuing commands that would exceed such limit.
	Status of This Memo		Status of This Memo
	This document is not an Internet Standards Track specification; it is		This document is not an Internet Standards Track specification; it is
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	not be created outside the IETF Standards Process, except to format		not be created outside the IETF Standards Process, except to format
	it for publication as an RFC or to translate it into languages other		it for publication as an RFC or to translate it into languages other
	than English.		than English.
	Table of Contents		Table of Contents
	1. Introduction and Overview		1. Introduction and Overview
	2. Document Conventions		2. Document Conventions
	3. The MESSAGELIMIT Extension		3. The MESSAGELIMIT Extension
	3.1. Returning Limits on the Number of Messages Processed in a		3.1. Returning Limits on the Number of Messages Processed in a
	Single SEARCH/FETCH/STORE/COPY/MOVE/APPEND/EXPUNGE Command		Single Command
	3.2. UIDAFTER and UIDBEFORE SEARCH Criteria		3.2. UIDAFTER and UIDBEFORE SEARCH Criteria
	3.3. Interaction with SORT and THREAD Extensions		3.3. Interaction with SORT and THREAD Extensions
	3.4. Interaction with SEARCHRES Extension and IMAP4rev2		3.4. Interaction with SEARCHRES Extension and IMAP4rev2
	4. Interoperability Considerations		4. Interoperability Considerations
	4.1. Effects of MESSAGELIMIT and SAVELIMIT Extensions on		4.1. Effects of MESSAGELIMIT and SAVELIMIT Extensions on
	Noncompliant Clients		Noncompliant Clients
	4.2. Maintaining Compatibility		4.2. Maintaining Compatibility
	5. Formal Syntax		5. Formal Syntax
	6. Security Considerations		6. Security Considerations
	7. IANA Considerations		7. IANA Considerations
	7.1. Additions to the IMAP Capabilities Registry		7.1. Additions to the IMAP Capabilities Registry
	8. References		8. References
	8.1. Normative References		8.1. Normative References
	8.2. Informative References		8.2. Informative References
	Acknowledgments		Acknowledgments
	Authors' Addresses		Authors' Addresses
	1. Introduction and Overview		1. Introduction and Overview
	This document defines an extension to the Internet Message Access		This document defines an extension to the Internet Message Access
	Protocol [RFC3501] for announcing a server limit on the number of		Protocol [RFC9051] for announcing a server limit on the number of
	messages that can be processed in a single FETCH, SEARCH, STORE,		messages that can be processed in a single FETCH, SEARCH, STORE,
	COPY, or MOVE command (or their UID variants), or a single APPEND or		COPY, or MOVE command (or their UID variants), or a single APPEND or
	UID EXPUNGE command. This extension is compatible with both		UID EXPUNGE command. This extension is compatible with both
	IMAP4rev1 [RFC3501] and IMAP4rev2 [RFC9051].		IMAP4rev1 [RFC3501] and IMAP4rev2 [RFC9051].
	2. Document Conventions		2. Document Conventions
	In protocol examples, this document uses a prefix of "C: " to denote		In protocol examples, this document uses a prefix of "C: " to denote
	lines sent by the client to the server, and "S: " for lines sent by		lines sent by the client to the server, and "S: " for lines sent by
	the server to the client. Lines prefixed with "// " are comments		the server to the client. Lines prefixed with "// " are comments
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	An IMAP server that only enforces the message limit on COPY and		An IMAP server that only enforces the message limit on COPY and
	APPEND commands (and their UID variants) would include the		APPEND commands (and their UID variants) would include the
	"SAVELIMIT=<limit>" capability (instead of the		"SAVELIMIT=<limit>" capability (instead of the
	"MESSAGELIMIT=<limit>") in the CAPABILITY response or response code.		"MESSAGELIMIT=<limit>") in the CAPABILITY response or response code.
	The limit advertised in the MESSAGELIMIT or SAVELIMIT capability		The limit advertised in the MESSAGELIMIT or SAVELIMIT capability
	SHOULD NOT be lower than 1000 messages.		SHOULD NOT be lower than 1000 messages.
	3.1. Returning Limits on the Number of Messages Processed in a Single		3.1. Returning Limits on the Number of Messages Processed in a Single
	SEARCH/FETCH/STORE/COPY/MOVE/APPEND/EXPUNGE Command		Command
	If a server implementation doesn't allow more than <N> messages to be		If a server implementation doesn't allow more than <N> messages to be
	operated on by a single COPY or UID COPY command, it MUST fail the		operated on by a single COPY or UID COPY command, it MUST fail the
	command by returning a tagged NO response with the MESSAGELIMIT		command by returning a tagged NO response with the MESSAGELIMIT
	response code defined below. No messages are copied in this case.		response code defined below. No messages are copied in this case.
	If a server implementation doesn't allow more than <N> messages to be		If a server implementation doesn't allow more than <N> messages to be
	operated on by a single SEARCH, FETCH, STORE, or MOVE command (or		operated on by a single SEARCH, FETCH, STORE, or MOVE command (or
	their UID variants), or an APPEND or UID EXPUNGE command, it MUST		their UID variants), or an APPEND or UID EXPUNGE command, it MUST
	return the MESSAGELIMIT response code defined below:		return the MESSAGELIMIT response code defined below:
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	partial results saved		partial results saved
	4. Interoperability Considerations		4. Interoperability Considerations
	4.1. Effects of MESSAGELIMIT and SAVELIMIT Extensions on Noncompliant		4.1. Effects of MESSAGELIMIT and SAVELIMIT Extensions on Noncompliant
	Clients		Clients
	A server that advertises the MESSAGELIMIT=N capability would have the		A server that advertises the MESSAGELIMIT=N capability would have the
	following effect on clients that don't support this capability:		following effect on clients that don't support this capability:
	* Operations on a mailbox that has <= N messages are not affected.		* Operations are not affected on a mailbox that has N messages or
			fewer.
	* In a mailbox with more than N messages:		* In a mailbox with more than N messages:
	- An attempt to COPY or UID COPY more than N messages will always		- An attempt to COPY or UID COPY more than N messages will always
	fail.		fail.
	- EXPUNGE and CLOSE will always operate on the full mailbox, so		- EXPUNGE and CLOSE will always operate on the full mailbox, so
	they are not affected.		they are not affected.
	- Other commands like FETCH, SEARCH, and MOVE will be effectively		- Other commands like FETCH, SEARCH, and MOVE will be effectively
	skipping to change at line 526 ¶		skipping to change at line 527 ¶
	[RFC9394] Melnikov, A., Achuthan, A. P., Nagulakonda, V., and L.		[RFC9394] Melnikov, A., Achuthan, A. P., Nagulakonda, V., and L.
	Alves, "IMAP PARTIAL Extension for Paged SEARCH and		Alves, "IMAP PARTIAL Extension for Paged SEARCH and
	FETCH", RFC 9394, DOI 10.17487/RFC9394, June 2023,		FETCH", RFC 9394, DOI 10.17487/RFC9394, June 2023,
	<https://www.rfc-editor.org/info/rfc9394>.		<https://www.rfc-editor.org/info/rfc9394>.
	Acknowledgments		Acknowledgments
	This document was motivated by the Yahoo! team and their questions		This document was motivated by the Yahoo! team and their questions
	about best client practices for dealing with large mailboxes.		about best client practices for dealing with large mailboxes.
	The editor of this document would like to thank the following people		The authors of this document would like to thank the following people
	who provided useful comments, contributed text, or participated in		who provided useful comments, contributed text, or participated in
	discussions of this document: Timo Sirainen, Barry Leiba, Ken		discussions of this document: Timo Sirainen, Barry Leiba, Ken
	Murchison, and Arnt Gulbrandsen.		Murchison, and Arnt Gulbrandsen.
	Authors' Addresses		Authors' Addresses
	Alexey Melnikov		Alexey Melnikov
	Isode Limited		Isode Limited
	Email: alexey.melnikov@isode.com		Email: alexey.melnikov@isode.com
	URI: https://www.isode.com		URI: https://www.isode.com
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