draft-ietf-uta-smtp-require-tls-03.txt		draft-ietf-uta-smtp-require-tls-04.txt
	Internet Engineering Task Force J. Fenton		Internet Engineering Task Force J. Fenton
	Internet-Draft Altmode Networks		Internet-Draft Altmode Networks
	Intended status: Standards Track June 22, 2018		Intended status: Standards Track September 26, 2018
	Expires: December 24, 2018		Expires: March 30, 2019
	SMTP Require TLS Option		SMTP Require TLS Option
	draft-ietf-uta-smtp-require-tls-03		draft-ietf-uta-smtp-require-tls-04
	Abstract		Abstract
	The SMTP STARTTLS option, used in negotiating transport-level		The SMTP STARTTLS option, used in negotiating transport-level
	encryption of SMTP connections, is not as useful from a security		encryption of SMTP connections, is not as useful from a security
	standpoint as it might be because of its opportunistic nature;		standpoint as it might be because of its opportunistic nature;
	message delivery is, by default, prioritized over security. This		message delivery is, by default, prioritized over security. This
	document describes an SMTP service extension, REQUIRETLS, and message		document describes an SMTP service extension, REQUIRETLS, and message
	header field, RequireTLS. If the REQUIRETLS option or RequireTLS		header field, RequireTLS. If the REQUIRETLS option or RequireTLS
	message header field is used when sending a message, it asserts a		message header field is used when sending a message, it asserts a
	skipping to change at page 1, line 41 ¶		skipping to change at page 1, line 41 ¶
	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 https://datatracker.ietf.org/drafts/current/.		Drafts is at https://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 December 24, 2018.		This Internet-Draft will expire on March 30, 2019.
	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
	(https://trustee.ietf.org/license-info) in effect on the date of		(https://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 29 ¶		skipping to change at page 2, line 29 ¶
	4.1. REQUIRETLS Receipt Requirements . . . . . . . . . . . . . 5		4.1. REQUIRETLS Receipt Requirements . . . . . . . . . . . . . 5
	4.2. REQUIRETLS Sender Requirements . . . . . . . . . . . . . 5		4.2. REQUIRETLS Sender Requirements . . . . . . . . . . . . . 5
	4.2.1. Sending with TLS Required . . . . . . . . . . . . . . 5		4.2.1. Sending with TLS Required . . . . . . . . . . . . . . 5
	4.2.2. Sending with TLS Optional . . . . . . . . . . . . . . 6		4.2.2. Sending with TLS Optional . . . . . . . . . . . . . . 6
	4.3. REQUIRETLS Submission . . . . . . . . . . . . . . . . . . 7		4.3. REQUIRETLS Submission . . . . . . . . . . . . . . . . . . 7
	4.4. Delivery of REQUIRETLS messages . . . . . . . . . . . . . 7		4.4. Delivery of REQUIRETLS messages . . . . . . . . . . . . . 7
	5. Non-delivery message handling . . . . . . . . . . . . . . . . 7		5. Non-delivery message handling . . . . . . . . . . . . . . . . 7
	6. Mailing list considerations . . . . . . . . . . . . . . . . . 8		6. Mailing list considerations . . . . . . . . . . . . . . . . . 8
	7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8		7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
	8. Security Considerations . . . . . . . . . . . . . . . . . . . 9		8. Security Considerations . . . . . . . . . . . . . . . . . . . 9
	8.1. Passive attacks . . . . . . . . . . . . . . . . . . . . . 10		8.1. Passive attacks . . . . . . . . . . . . . . . . . . . . . 9
	8.2. Active attacks . . . . . . . . . . . . . . . . . . . . . 10		8.2. Active attacks . . . . . . . . . . . . . . . . . . . . . 10
	8.3. Bad Actor MTAs . . . . . . . . . . . . . . . . . . . . . 10		8.3. Bad Actor MTAs . . . . . . . . . . . . . . . . . . . . . 10
	9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 11		9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 10
	10. Revision History . . . . . . . . . . . . . . . . . . . . . . 11		10. Revision History . . . . . . . . . . . . . . . . . . . . . . 11
	10.1. Changes since -02 Draft . . . . . . . . . . . . . . . . 11		10.1. Changes since -03 Draft . . . . . . . . . . . . . . . . 11
	10.2. Changes since -01 Draft . . . . . . . . . . . . . . . . 11		10.2. Changes since -02 Draft . . . . . . . . . . . . . . . . 11
	10.3. Changes since -00 Draft . . . . . . . . . . . . . . . . 11		10.3. Changes since -01 Draft . . . . . . . . . . . . . . . . 11
	10.4. Changes since fenton-03 Draft . . . . . . . . . . . . . 11		10.4. Changes since -00 Draft . . . . . . . . . . . . . . . . 11
	10.5. Changes Since -02 Draft . . . . . . . . . . . . . . . . 12		10.5. Changes since fenton-03 Draft . . . . . . . . . . . . . 12
	10.6. Changes Since -01 Draft . . . . . . . . . . . . . . . . 12		10.6. Changes Since -02 Draft . . . . . . . . . . . . . . . . 12
	10.7. Changes Since -00 Draft . . . . . . . . . . . . . . . . 12		10.7. Changes Since -01 Draft . . . . . . . . . . . . . . . . 12
	11. References . . . . . . . . . . . . . . . . . . . . . . . . . 12		10.8. Changes Since -00 Draft . . . . . . . . . . . . . . . . 12
	11.1. Normative References . . . . . . . . . . . . . . . . . . 12		11. References . . . . . . . . . . . . . . . . . . . . . . . . . 13
			11.1. Normative References . . . . . . . . . . . . . . . . . . 13
	11.2. Informative References . . . . . . . . . . . . . . . . . 14		11.2. Informative References . . . . . . . . . . . . . . . . . 14
	Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 14		Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 14
	1. Introduction		1. Introduction
	The SMTP [RFC5321] STARTTLS service extension [RFC3207] provides a		The SMTP [RFC5321] STARTTLS service extension [RFC3207] provides a
	means by which an SMTP server and client can establish a Transport		means by which an SMTP server and client can establish a Transport
	Layer Security (TLS) protected session for the transmission of email		Layer Security (TLS) protected session for the transmission of email
	messages. By default, TLS is used only upon mutual agreement		messages. By default, TLS is used only upon mutual agreement
	(successful negotiation) of STARTTLS between the client and server;		(successful negotiation) of STARTTLS between the client and server;
	if this is not possible, the message is sent without transport		if this is not possible, the message is sent without transport
	encryption. Furthermore, it is common practice for the client to		encryption. Furthermore, it is common practice for the client to
	negotiate TLS even if the SMTP server's certificate is invalid.		negotiate TLS even if the SMTP server's certificate is invalid.
	Policy mechanisms such as DANE [RFC7672] and MTA-STS		Policy mechanisms such as DANE [RFC7672] and MTA-STS [RFC8461] may
	[I-D.ietf-uta-mta-sts] may impose requirements for the use of TLS for		impose requirements for the use of TLS for email destined for some
	email destined for some domains. However, such policies do not allow		domains. However, such policies do not allow the sender to specify
	the sender to specify which messages are more sensitive and require		which messages are more sensitive and require transport-level
	transport-level encryption, and which ones are less sensitive and		encryption, and which ones are less sensitive and ought to be relayed
	ought to be relayed even if TLS cannot be negotiated successfully.		even if TLS cannot be negotiated successfully.
	The default opportunistic nature of SMTP TLS enables several "on the		The default opportunistic nature of SMTP TLS enables several "on the
	wire" attacks on SMTP security between MTAs. These include passive		wire" attacks on SMTP security between MTAs. These include passive
	eavesdropping on connections for which TLS is not used, interference		eavesdropping on connections for which TLS is not used, interference
	in the SMTP protocol to prevent TLS from being negotiated (presumably		in the SMTP protocol to prevent TLS from being negotiated (presumably
	accompanied by eavesdropping), and insertion of a man-in-the-middle		accompanied by eavesdropping), and insertion of a man-in-the-middle
	attacker exploiting the lack of server authentication by the client.		attacker exploiting the lack of server authentication by the client.
	Attacks are described in more detail in the Security Considerations		Attacks are described in more detail in the Security Considerations
	section of this document.		section of this document.
	skipping to change at page 4, line 14 ¶		skipping to change at page 4, line 14 ¶
	2. The REQUIRETLS Service Extension		2. The REQUIRETLS Service Extension
	1. The textual name of the extension is "Require TLS".		1. The textual name of the extension is "Require TLS".
	2. The EHLO keyword value associated with this extension is		2. The EHLO keyword value associated with this extension is
	"REQUIRETLS".		"REQUIRETLS".
	3. One MAIL FROM option is defined by this extension.		3. One MAIL FROM option is defined by this extension.
	4. Two new SMTP status codes are defined by this extension to convey		4. One new SMTP status code is defined by this extension to convey
	error conditions resulting from failure of the client to		an error condition resulting from failure of the client to send
	negotiate a TLS connection with the required security and as a		to a server not also supporting the REQUIRETLS extension.
	result of an attempt to send to a server not also supporting the
	REQUIRETLS extension.
	In order to specify REQUIRETLS treatment for a given message, the		In order to specify REQUIRETLS treatment for a given message, the
	REQUIRETLS option is specified on the MAIL FROM command when that		REQUIRETLS option is specified on the MAIL FROM command when that
	message is transmitted. This option MUST only be specified in the		message is transmitted. This option MUST only be specified in the
	context of an SMTP session meeting the security requirements that		context of an SMTP session meeting the security requirements that
	have been specified:		have been specified:
	o The session itself MUST employ TLS transmission.		o The session itself MUST employ TLS transmission.
	o The certificate presented by the SMTP server MUST either verify		o The certificate presented by the SMTP server MUST either verify
	skipping to change at page 4, line 43 ¶		skipping to change at page 4, line 41 ¶
	client.		client.
	o Following the negotiation of STARTTLS, the SMTP server MUST		o Following the negotiation of STARTTLS, the SMTP server MUST
	advertise in the subsequent EHLO response that it supports		advertise in the subsequent EHLO response that it supports
	REQUIRETLS.		REQUIRETLS.
	3. The RequireTLS Header Field		3. The RequireTLS Header Field
	One new message header field, RequireTLS, is defined by this		One new message header field, RequireTLS, is defined by this
	specification. It is used for messages requesting that recipient TLS		specification. It is used for messages requesting that recipient TLS
	policy (MTA-STS [I-D.ietf-uta-mta-sts] or DANE [RFC7672]) be ignored.		policy (including MTA-STS [RFC8461] and DANE [RFC7672]) be ignored.
	The RequireTLS header field has a single REQUIRED parameter:		The RequireTLS header field has a single REQUIRED parameter:
	o NO - The SMTP client SHOULD attempt to send the message regardless		o NO - The SMTP client SHOULD attempt to send the message regardless
	of its ability to negotiate STARTTLS with the SMTP server,		of its ability to negotiate STARTTLS with the SMTP server,
	ignoring policy-based mechanisms, if any, asserted by the		ignoring policy-based mechanisms (including MTA-STS and DANE), if
	recipient domain. Nevertheless, the client SHOULD negotiate		any, asserted by the recipient domain. Nevertheless, the client
	STARTTLS with the server if available.		SHOULD negotiate STARTTLS with the server if available.
	More than one instance of the RequireTLS header field MUST NOT appear		More than one instance of the RequireTLS header field MUST NOT appear
	in a given message.		in a given message.
	4. REQUIRETLS Semantics		4. REQUIRETLS Semantics
	4.1. REQUIRETLS Receipt Requirements		4.1. REQUIRETLS Receipt Requirements
	Upon receipt of the REQUIRETLS option on a MAIL FROM command during		Upon receipt of the REQUIRETLS option on a MAIL FROM command during
	the receipt of a message, an SMTP server MUST tag that message as		the receipt of a message, an SMTP server MUST tag that message as
	skipping to change at page 5, line 44 ¶		skipping to change at page 5, line 41 ¶
	MTA MUST:		MTA MUST:
	1. Look up the SMTP server to which the message is to be sent as		1. Look up the SMTP server to which the message is to be sent as
	described in [RFC5321] Section 5.1.		described in [RFC5321] Section 5.1.
	2. Open an SMTP session with the peer SMTP server using the EHLO		2. Open an SMTP session with the peer SMTP server using the EHLO
	verb.		verb.
	3. Establish a TLS-protected SMTP session with its peer SMTP server		3. Establish a TLS-protected SMTP session with its peer SMTP server
	and authenticate the server's certificate as specified in		and authenticate the server's certificate as specified in
	[RFC6125] or [RFC6698] as applicable.		[RFC6125] or [RFC7672] as applicable.
	4. Ensure that the response to the subsequent EHLO following		4. Ensure that the response to the subsequent EHLO following
	establishment of the TLS protection advertises the REQUIRETLS		establishment of the TLS protection advertises the REQUIRETLS
	capability.		capability.
	5. The SMTP client SHOULD also require that meaningfully secure		5. The SMTP client SHOULD also require that meaningfully secure
	cipher algorithms and key lengths be negotiated with the server.		cipher algorithms and key lengths be negotiated with the server.
	The choices of key lengths and algorithms change over time, so a		The choices of key lengths and algorithms change over time, so a
	specific requirement is not presented here.		specific requirement is not presented here.
	If any of the above steps fail, the client MUST issue a QUIT to the		If any of the above steps fail, the client MUST issue a QUIT to the
	server and repeat steps 2-4 with each host on the recipient domain's		server and repeat steps 2-4 with each host on the recipient domain's
	list of MX hosts in an attempt to find a mail path that meets the		list of MX hosts in an attempt to find a mail path that meets the
	sender's requirements. The client MAY send other, unprotected,		sender's requirements. The client MAY send other, unprotected,
	messages to that server if it has any prior to issuing the QUIT. If		messages to that server if it has any prior to issuing the QUIT. If
	there are no more MX hosts, the client MUST NOT transmit the message		there are no more MX hosts, the client MUST NOT transmit the message
	to the domain.		to the domain.
	skipping to change at page 8, line 41 ¶		skipping to change at page 8, line 37 ¶
	messages to the resulting messages they originate. If this is done,		messages to the resulting messages they originate. If this is done,
	they SHOULD also apply these requirements to administrative traffic,		they SHOULD also apply these requirements to administrative traffic,
	such as messages to moderators requesting approval of messages.		such as messages to moderators requesting approval of messages.
	7. IANA Considerations		7. IANA Considerations
	If published as an RFC, this draft requests the addition of the		If published as an RFC, this draft requests the addition of the
	following keyword to the SMTP Service Extensions Registry		following keyword to the SMTP Service Extensions Registry
	[MailParams]:		[MailParams]:
	Textual name: RequireTLS		Textual name: RequireTLS
	EHLO keyword value: REQUIRETLS		EHLO keyword value: REQUIRETLS
	Syntax and parameters: (no parameters)		Syntax and parameters: (no parameters)
	Additional SMTP verbs: none		Additional SMTP verbs: none
	MAIL and RCPT parameters: REQUIRETLS parameter on MAIL		MAIL and RCPT parameters: REQUIRETLS parameter on MAIL
	Behavior: Use of the REQUIRETLS parameter on the		Behavior: Use of the REQUIRETLS parameter on the
	MAIL verb causes that message to require		MAIL verb causes that message to require
	the use of TLS and tagging with REQUIRETLS		the use of TLS and tagging with
	for all onward relay.		REQUIRETLS for all onward relay.
	Command length increment: 11 characters		Command length increment: 11 characters
	If published as an RFC, this draft requests the addition of an entry		If published as an RFC, this draft requests the addition of an entry
	to the Simple Mail Transfer Protocol (SMTP) Enhanced Status Codes		to the Simple Mail Transfer Protocol (SMTP) Enhanced Status Codes
	Registry [SMTPStatusCodes]:		Registry [SMTPStatusCodes]:
	Code: 5.7.YYY		Code: 5.7.YYY
	Sample Text: REQUIRETLS support required		Sample Text: REQUIRETLS support required
	Associated basic status code: 530		Associated basic status code: 530
	Description: This indicates that the message was not		Description: This indicates that the message was not
	able to be forwarded because it was		able to be forwarded because it was
	received with a REQUIRETLS requirement		received with a REQUIRETLS requirement
	skipping to change at page 11, line 16 ¶		skipping to change at page 11, line 9 ¶
	The author would like to acknowledge many helpful suggestions on the		The author would like to acknowledge many helpful suggestions on the
	ietf-smtp and uta mailing lists, in particular those of Viktor		ietf-smtp and uta mailing lists, in particular those of Viktor
	Dukhovni, Chris Newman, Tony Finch, Jeremy Harris, Arvel Hathcock,		Dukhovni, Chris Newman, Tony Finch, Jeremy Harris, Arvel Hathcock,
	John Klensin, John Levine, Rolf Sonneveld, and Per Thorsheim.		John Klensin, John Levine, Rolf Sonneveld, and Per Thorsheim.
	10. Revision History		10. Revision History
	To be removed by RFC Editor upon publication as an RFC.		To be removed by RFC Editor upon publication as an RFC.
	10.1. Changes since -02 Draft		10.1. Changes since -03 Draft
			Working Group Last Call changes, including:
			o Correct reference for SMTP DANE
			o Clarify that RequireTLS: NO applies to both MTA-STS and DANE
			policies
			o Correct newly-defined status codes
			o Update MTA-STS references to RFC
			10.2. Changes since -02 Draft
	o More complete documentation for IANA registration requests.		o More complete documentation for IANA registration requests.
	o Changed bounce handling to use RET parameters of RFC 3461, along		o Changed bounce handling to use RET parameters of RFC 3461, along
	with slightly more liberal transmission of bounces even if		with slightly more liberal transmission of bounces even if
	REQUIRETLS can't be negotiated.		REQUIRETLS can't be negotiated.
	10.2. Changes since -01 Draft		10.3. Changes since -01 Draft
	o Converted DEEP references to RFC 8314.		o Converted DEEP references to RFC 8314.
	o Removed REQUIRETLS options: CHAIN, DANE, and DNSSEC.		o Removed REQUIRETLS options: CHAIN, DANE, and DNSSEC.
	o Editorial corrections, notably making the header field name		o Editorial corrections, notably making the header field name
	consistent (RequireTLS rather than Require-TLS).		consistent (RequireTLS rather than Require-TLS).
	10.3. Changes since -00 Draft		10.4. Changes since -00 Draft
	o Created new header field, Require-TLS, for use by "NO" option.		o Created new header field, Require-TLS, for use by "NO" option.
	o Removed "NO" option from SMTP service extension.		o Removed "NO" option from SMTP service extension.
	o Recommend DEEP requirements for delivery of messages requiring		o Recommend DEEP requirements for delivery of messages requiring
	TLS.		TLS.
	o Assorted copy edits		o Assorted copy edits
	10.4. Changes since fenton-03 Draft		10.5. Changes since fenton-03 Draft
	o Wording improvements from Rolf Sonneveld review 22 July 2017		o Wording improvements from Rolf Sonneveld review 22 July 2017
	o A few copy edits		o A few copy edits
	o Conversion from individual to UTA WG draft		o Conversion from individual to UTA WG draft
	10.5. Changes Since -02 Draft		10.6. Changes Since -02 Draft
	o Incorporation of "MAY TLS" functionality as REQUIRETLS=NO per		o Incorporation of "MAY TLS" functionality as REQUIRETLS=NO per
	suggestion on UTA WG mailing list.		suggestion on UTA WG mailing list.
	o Additional guidance on bounce messages		o Additional guidance on bounce messages
	10.6. Changes Since -01 Draft		10.7. Changes Since -01 Draft
	o Specified retries when multiple MX hosts exist for a given domain.		o Specified retries when multiple MX hosts exist for a given domain.
	o Clarified generation of non-delivery messages		o Clarified generation of non-delivery messages
	o Specified requirements for application of REQUIRETLS to mail		o Specified requirements for application of REQUIRETLS to mail
	forwarders and mailing lists.		forwarders and mailing lists.
	o Clarified DNSSEC requirements to include MX lookup only.		o Clarified DNSSEC requirements to include MX lookup only.
	o Corrected terminology regarding message retrieval vs. delivery.		o Corrected terminology regarding message retrieval vs. delivery.
	o Changed category to standards track.		o Changed category to standards track.
	10.7. Changes Since -00 Draft		10.8. Changes Since -00 Draft
	o Conversion of REQUIRETLS from an SMTP verb to a MAIL FROM		o Conversion of REQUIRETLS from an SMTP verb to a MAIL FROM
	parameter to better associate REQUIRETLS requirements with		parameter to better associate REQUIRETLS requirements with
	transmission of individual messages.		transmission of individual messages.
	o Addition of an option to require DNSSEC lookup of the remote mail		o Addition of an option to require DNSSEC lookup of the remote mail
	server, since this affects the common name of the certificate that		server, since this affects the common name of the certificate that
	is presented.		is presented.
	o Clarified the wording to more clearly state that TLS sessions must		o Clarified the wording to more clearly state that TLS sessions must
	skipping to change at page 13, line 41 ¶		skipping to change at page 13, line 50 ¶
	DOI 10.17487/RFC5321, October 2008,		DOI 10.17487/RFC5321, October 2008,
	<https://www.rfc-editor.org/info/rfc5321>.		<https://www.rfc-editor.org/info/rfc5321>.
	[RFC6125] Saint-Andre, P. and J. Hodges, "Representation and		[RFC6125] Saint-Andre, P. and J. Hodges, "Representation and
	Verification of Domain-Based Application Service Identity		Verification of Domain-Based Application Service Identity
	within Internet Public Key Infrastructure Using X.509		within Internet Public Key Infrastructure Using X.509
	(PKIX) Certificates in the Context of Transport Layer		(PKIX) Certificates in the Context of Transport Layer
	Security (TLS)", RFC 6125, DOI 10.17487/RFC6125, March		Security (TLS)", RFC 6125, DOI 10.17487/RFC6125, March
	2011, <https://www.rfc-editor.org/info/rfc6125>.		2011, <https://www.rfc-editor.org/info/rfc6125>.
	[RFC6698] Hoffman, P. and J. Schlyter, "The DNS-Based Authentication
	of Named Entities (DANE) Transport Layer Security (TLS)
	Protocol: TLSA", RFC 6698, DOI 10.17487/RFC6698, August
	2012, <https://www.rfc-editor.org/info/rfc6698>.
	[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC		[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
	2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,		2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
	May 2017, <https://www.rfc-editor.org/info/rfc8174>.		May 2017, <https://www.rfc-editor.org/info/rfc8174>.
	[RFC8314] Moore, K. and C. Newman, "Cleartext Considered Obsolete:		[RFC8314] Moore, K. and C. Newman, "Cleartext Considered Obsolete:
	Use of Transport Layer Security (TLS) for Email Submission		Use of Transport Layer Security (TLS) for Email Submission
	and Access", RFC 8314, DOI 10.17487/RFC8314, January 2018,		and Access", RFC 8314, DOI 10.17487/RFC8314, January 2018,
	<https://www.rfc-editor.org/info/rfc8314>.		<https://www.rfc-editor.org/info/rfc8314>.
	[SMTPStatusCodes]		[SMTPStatusCodes]
	Internet Assigned Numbers Authority (IANA), "Simple Mail		Internet Assigned Numbers Authority (IANA), "Simple Mail
	Transfer Protocol (SMTP) Enhanced Status Codes Registry",		Transfer Protocol (SMTP) Enhanced Status Codes Registry",
	2008, <http://www.iana.org/assignments/		2008, <http://www.iana.org/assignments/
	smtp-enhanced-status-codes>.		smtp-enhanced-status-codes>.
	11.2. Informative References		11.2. Informative References
	[I-D.ietf-uta-mta-sts]
	Margolis, D., Risher, M., Ramakrishnan, B., Brotman, A.,
	and J. Jones, "SMTP MTA Strict Transport Security (MTA-
	STS)", draft-ietf-uta-mta-sts-21 (work in progress), June
	2018.
	[RFC1939] Myers, J. and M. Rose, "Post Office Protocol - Version 3",		[RFC1939] Myers, J. and M. Rose, "Post Office Protocol - Version 3",
	STD 53, RFC 1939, DOI 10.17487/RFC1939, May 1996,		STD 53, RFC 1939, DOI 10.17487/RFC1939, May 1996,
	<https://www.rfc-editor.org/info/rfc1939>.		<https://www.rfc-editor.org/info/rfc1939>.
	[RFC3501] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION		[RFC3501] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION
	4rev1", RFC 3501, DOI 10.17487/RFC3501, March 2003,		4rev1", RFC 3501, DOI 10.17487/RFC3501, March 2003,
	<https://www.rfc-editor.org/info/rfc3501>.		<https://www.rfc-editor.org/info/rfc3501>.
	[RFC4880] Callas, J., Donnerhacke, L., Finney, H., Shaw, D., and R.		[RFC4880] Callas, J., Donnerhacke, L., Finney, H., Shaw, D., and R.
	Thayer, "OpenPGP Message Format", RFC 4880,		Thayer, "OpenPGP Message Format", RFC 4880,
	skipping to change at page 14, line 48 ¶		skipping to change at page 14, line 42 ¶
	Mail Extensions (S/MIME) Version 3.2 Message		Mail Extensions (S/MIME) Version 3.2 Message
	Specification", RFC 5751, DOI 10.17487/RFC5751, January		Specification", RFC 5751, DOI 10.17487/RFC5751, January
	2010, <https://www.rfc-editor.org/info/rfc5751>.		2010, <https://www.rfc-editor.org/info/rfc5751>.
	[RFC7672] Dukhovni, V. and W. Hardaker, "SMTP Security via		[RFC7672] Dukhovni, V. and W. Hardaker, "SMTP Security via
	Opportunistic DNS-Based Authentication of Named Entities		Opportunistic DNS-Based Authentication of Named Entities
	(DANE) Transport Layer Security (TLS)", RFC 7672,		(DANE) Transport Layer Security (TLS)", RFC 7672,
	DOI 10.17487/RFC7672, October 2015,		DOI 10.17487/RFC7672, October 2015,
	<https://www.rfc-editor.org/info/rfc7672>.		<https://www.rfc-editor.org/info/rfc7672>.
			[RFC8461] Margolis, D., Risher, M., Ramakrishnan, B., Brotman, A.,
			and J. Jones, "SMTP MTA Strict Transport Security (MTA-
			STS)", RFC 8461, DOI 10.17487/RFC8461, September 2018,
			<https://www.rfc-editor.org/info/rfc8461>.
	Author's Address		Author's Address
	Jim Fenton		Jim Fenton
	Altmode Networks		Altmode Networks
	Los Altos, California 94024		Los Altos, California 94024
	USA		USA
	Email: fenton@bluepopcorn.net		Email: fenton@bluepopcorn.net
End of changes. 23 change blocks.
	60 lines changed or deleted		66 lines changed or added
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