draft-ietf-uta-smtp-tlsrpt-04.txt   draft-ietf-uta-smtp-tlsrpt-05.txt 
Using TLS in Applications D. Margolis Using TLS in Applications D. Margolis
Internet-Draft Google, Inc Internet-Draft Google, Inc
Intended status: Standards Track A. Brotman Intended status: Standards Track A. Brotman
Expires: October 5, 2017 Comcast, Inc Expires: November 4, 2017 Comcast, Inc
B. Ramakrishnan B. Ramakrishnan
Yahoo!, Inc Yahoo!, Inc
J. Jones J. Jones
Microsoft, Inc Microsoft, Inc
M. Risher M. Risher
Google, Inc Google, Inc
April 3, 2017 May 3, 2017
SMTP TLS Reporting SMTP TLS Reporting
draft-ietf-uta-smtp-tlsrpt-04 draft-ietf-uta-smtp-tlsrpt-05
Abstract Abstract
A number of protocols exist for establishing encrypted channels A number of protocols exist for establishing encrypted channels
between SMTP Mail Transfer Agents, including STARTTLS [RFC3207], DANE between SMTP Mail Transfer Agents, including STARTTLS [RFC3207], DANE
[RFC6698], and MTA-STS (TODO: Add ref). These protocols can fail due [RFC6698], and MTA-STS (TODO: Add ref). These protocols can fail due
to misconfiguration or active attack, leading to undelivered messages to misconfiguration or active attack, leading to undelivered messages
or delivery over unencrypted or unauthenticated channels. This or delivery over unencrypted or unauthenticated channels. This
document describes a reporting mechanism and format by which sending document describes a reporting mechanism and format by which sending
systems can share statistics and specific information about potential systems can share statistics and specific information about potential
skipping to change at page 1, line 46 skipping to change at page 1, line 46
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 October 5, 2017. This Internet-Draft will expire on November 4, 2017.
Copyright Notice Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the Copyright (c) 2017 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
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described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2. Related Technologies . . . . . . . . . . . . . . . . . . . . 4 2. Related Technologies . . . . . . . . . . . . . . . . . . . . 4
3. Reporting Policy . . . . . . . . . . . . . . . . . . . . . . 4 3. Reporting Policy . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Example Reporting Policy . . . . . . . . . . . . . . . . 5 3.1. Example Reporting Policy . . . . . . . . . . . . . . . . 5
3.1.1. Report using MAILTO . . . . . . . . . . . . . . . . . 5 3.1.1. Report using MAILTO . . . . . . . . . . . . . . . . . 5
3.1.2. Report using HTTPS . . . . . . . . . . . . . . . . . 5 3.1.2. Report using HTTPS . . . . . . . . . . . . . . . . . 6
4. Reporting Schema . . . . . . . . . . . . . . . . . . . . . . 5 4. Reporting Schema . . . . . . . . . . . . . . . . . . . . . . 6
4.1. Report Time-frame . . . . . . . . . . . . . . . . . . . . 6 4.1. Report Time-frame . . . . . . . . . . . . . . . . . . . . 7
4.2. Delivery Summary . . . . . . . . . . . . . . . . . . . . 6 4.2. Delivery Summary . . . . . . . . . . . . . . . . . . . . 7
4.2.1. Success Count . . . . . . . . . . . . . . . . . . . . 6 4.2.1. Success Count . . . . . . . . . . . . . . . . . . . . 7
4.2.2. Failure Count . . . . . . . . . . . . . . . . . . . . 7 4.2.2. Failure Count . . . . . . . . . . . . . . . . . . . . 7
4.3. Result Types . . . . . . . . . . . . . . . . . . . . . . 7 4.3. Result Types . . . . . . . . . . . . . . . . . . . . . . 7
4.3.1. Negotiation Failures . . . . . . . . . . . . . . . . 7 4.3.1. Negotiation Failures . . . . . . . . . . . . . . . . 7
4.3.2. Policy Failures . . . . . . . . . . . . . . . . . . . 7 4.3.2. Policy Failures . . . . . . . . . . . . . . . . . . . 8
4.3.3. General Failures . . . . . . . . . . . . . . . . . . 8 4.3.3. General Failures . . . . . . . . . . . . . . . . . . 8
4.3.4. Transient Failures . . . . . . . . . . . . . . . . . 8 4.3.4. Transient Failures . . . . . . . . . . . . . . . . . 8
5. Report Delivery . . . . . . . . . . . . . . . . . . . . . . . 8 5. Report Delivery . . . . . . . . . . . . . . . . . . . . . . . 9
5.1. Report Filename . . . . . . . . . . . . . . . . . . . . . 8 5.1. Report Filename . . . . . . . . . . . . . . . . . . . . . 9
5.2. Compression . . . . . . . . . . . . . . . . . . . . . . . 9 5.2. Compression . . . . . . . . . . . . . . . . . . . . . . . 9
5.3. Email Transport . . . . . . . . . . . . . . . . . . . . . 9 5.3. Email Transport . . . . . . . . . . . . . . . . . . . . . 10
5.4. HTTPS Transport . . . . . . . . . . . . . . . . . . . . . 10 5.4. HTTPS Transport . . . . . . . . . . . . . . . . . . . . . 10
5.5. Delivery Retry . . . . . . . . . . . . . . . . . . . . . 10 5.5. Delivery Retry . . . . . . . . . . . . . . . . . . . . . 11
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
7. Security Considerations . . . . . . . . . . . . . . . . . . . 11 7. Security Considerations . . . . . . . . . . . . . . . . . . . 11
8. Appendix 1: Example Reporting Policy . . . . . . . . . . . . 11 8. Appendix 1: Example Reporting Policy . . . . . . . . . . . . 12
8.1. Report using MAILTO . . . . . . . . . . . . . . . . . . . 11 8.1. Report using MAILTO . . . . . . . . . . . . . . . . . . . 12
8.2. Report using HTTPS . . . . . . . . . . . . . . . . . . . 12 8.2. Report using HTTPS . . . . . . . . . . . . . . . . . . . 12
9. Appendix 2: JSON Report Schema . . . . . . . . . . . . . . . 12 9. Appendix 2: JSON Report Schema . . . . . . . . . . . . . . . 12
10. Appendix 3: Example JSON Report . . . . . . . . . . . . . . . 14 10. Appendix 3: Example JSON Report . . . . . . . . . . . . . . . 15
11. Normative References . . . . . . . . . . . . . . . . . . . . 16 11. Normative References . . . . . . . . . . . . . . . . . . . . 16
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 17 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 17
1. Introduction 1. Introduction
The STARTTLS extension to SMTP [RFC3207] allows SMTP clients and The STARTTLS extension to SMTP [RFC3207] allows SMTP clients and
hosts to establish secure SMTP sessions over TLS. The protocol hosts to establish secure SMTP sessions over TLS. The protocol
design is based on "Opportunistic Security" (OS) [RFC7435], which design is based on "Opportunistic Security" (OS) [RFC7435], which
maintains interoperability with clients that do not support STARTTLS maintains interoperability with clients that do not support STARTTLS
but means that any attacker who can delete parts of the SMTP session but means that any attacker who can delete parts of the SMTP session
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o Policy Domain: The domain against which an MTA-STS or DANE Policy o Policy Domain: The domain against which an MTA-STS or DANE Policy
is defined. is defined.
o Sending MTA: The MTA initiating the delivery of an email message. o Sending MTA: The MTA initiating the delivery of an email message.
2. Related Technologies 2. Related Technologies
o This document is intended as a companion to the specification for o This document is intended as a companion to the specification for
SMTP MTA Strict Transport Security (MTA-STS, TODO: Add ref). SMTP MTA Strict Transport Security (MTA-STS, TODO: Add ref).
o The Public Key Pinning Extension for HTTP [RFC7469] contains a o SMTP-TLSRPT defines a mechanism for sending domains that are
JSON-based definition for reporting individual pin validation compatible with MTA-STS or DANE to share success and failure
failures. statistics with recipient domains. DANE is defined in [RFC6698]
and MTA-STS is defined in [TODO]
o The Domain-based Message Authentication, Reporting, and
Conformance (DMARC) [RFC7489] contains an XML-based reporting
format for aggregate and detailed email delivery errors.
3. Reporting Policy 3. Reporting Policy
A domain publishes a record to its DNS indicating that it wishes to A domain publishes a record to its DNS indicating that it wishes to
receive reports. These SMTP TLSRPT policies are distributed via DNS receive reports. These SMTP TLSRPT policies are distributed via DNS
from the Policy Domain's zone, as TXT records (similar to DMARC from the Policy Domain's zone, as TXT records (similar to DMARC
policies) under the name "_smtp-tlsrpt". For example, for the Policy policies) under the name "_smtp-tlsrpt". For example, for the Policy
Domain "example.com", the recipient's TLSRPT policy can be retrieved Domain "example.com", the recipient's TLSRPT policy can be retrieved
from "_smtp-tlsrpt.example.com". from "_smtp-tlsrpt.example.com".
Policies consist of the following directives: Policies consist of the following directives:
o "v": This value MUST be equal to "TLSRPTv1". o "v": This value MUST be equal to "TLSRPTv1".
o "rua": A URI specifying the endpoint to which aggregate o "rua": A URI specifying the endpoint to which aggregate
information about policy failures should be sent (see the section information about policy failures should be sent (see Section 4,
_Reporting_ _Schema_ for more information). Two URI schemes are "Reporting Schema", for more information). Two URI schemes are
supported: "mailto" and "https". supported: "mailto" and "https".
* In the case of "https", reports should be submitted via POST o In the case of "https", reports should be submitted via POST
([RFC2818]) to the specified URI. ([RFC2818]) to the specified URI.
* In the case of "mailto", reports should be submitted to the o In the case of "mailto", reports should be submitted to the
specified email address. When sending failure reports via specified email address ([RFC6068]). When sending failure reports
SMTP, sending MTAs MUST deliver reports despite any TLS-related via SMTP, sending MTAs MUST deliver reports despite any TLS-
failures. This may mean that the reports are delivered in the related failures. This may mean that the reports are delivered in
clear. the clear.
The formal definition of the "_smtp-tlsrpt" TXT record, defined using The formal definition of the "_smtp-tlsrpt" TXT record, defined using
[RFC5234], is as follows: [RFC5234], is as follows:
tlsrpt-record = tlsrpt-version *WSP %x3B tlsrpt-rua tlsrpt-record = tlsrpt-version *WSP field-delim *WSP tlsrpt-rua
[field-delim [tlsrpt-extensions]]
tlsrpt-version = "v" *WSP "=" *WSP %x54 %x4C %x53 field-delim = %x3B ; ";"
%x52 %x50 %x54 %x76 %x31
tlsrpt-rua = "rua" *WSP "=" *WSP tlsrpt-uri tlsrpt-version = %x76 *WSP "=" *WSP %x54 %x4C %x53 %x52
%x50 %x54 %x76 %x31 ; "v=TSRPTv1"
tlsrpt-uri = URI tlsrpt-rua = %x72 %x75 %x61 *WSP "=" *WSP tlsrpt-uri ; "rua=..."
; "URI" is imported from [@!RFC3986]; commas (ASCII
; 0x2C) and exclamation points (ASCII 0x21) tlsrpt-uri = URI
; MUST be encoded; the numeric portion MUST fit ; "URI" is imported from [@!RFC3986]; commas (ASCII
; within an unsigned 64-bit integer ; 0x2C) and exclamation points (ASCII 0x21)
; MUST be encoded; the numeric portion MUST fit
; within an unsigned 64-bit integer
tlsrpt-extensions = tlsrpt-extension *(field-delim tlsrpt-extension)
[field-delim]
; extension fields
tlsrpt-extension = tlsrpt-ext-name *WSP "=" *WSP tlsrpt-ext-value
tlsrpt-ext-name = (ALPHA / DIGIT) *31(ALPHA / DIGIT / "_" / "-" / ".")
tlsrpt-ext-value = 1*(%x21-3A / %x3C / %x3E-7E) ; chars excluding
; "=", ";", SP, and
; control chars
If multiple TXT records for "_smtp-tlsrpt" are returned by the If multiple TXT records for "_smtp-tlsrpt" are returned by the
resolver, records which do not begin with "v=TLSRPTv1;" are resolver, records which do not begin with "v=TLSRPTv1;" are
discarded. If the number of resulting records is not one, senders discarded. If the number of resulting records is not one, senders
MUST assume the recipient domain does not implement TLSRPT. MUST assume the recipient domain does not implement TLSRPT. Parsers
MUST accept TXT records which are syntactically valid (i.e. valid
key-value pairs seprated by semi-colons) and implementing a superset
of this specification, in which case unknown fields SHALL be ignored.
3.1. Example Reporting Policy 3.1. Example Reporting Policy
3.1.1. Report using MAILTO 3.1.1. Report using MAILTO
_smtp-tlsrpt.example.com. IN TXT \ _smtp-tlsrpt.example.com. IN TXT \
"v=TLSRPTv1;rua=mailto:reports@example.com" "v=TLSRPTv1;rua=mailto:reports@example.com"
3.1.2. Report using HTTPS 3.1.2. Report using HTTPS
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successfully negotiate a policy-compliant TLS connection, and successfully negotiate a policy-compliant TLS connection, and
serves to provide a "heartbeat" to receiving domains that serves to provide a "heartbeat" to receiving domains that
reporting is functional and tabulating correctly. This field reporting is functional and tabulating correctly. This field
contains an aggregate count of successful connections for the contains an aggregate count of successful connections for the
reporting system. reporting system.
4.2.2. Failure Count 4.2.2. Failure Count
o "failure-count": This indicates that the sending MTA was unable to o "failure-count": This indicates that the sending MTA was unable to
successfully establish a connection with the receiving platform. successfully establish a connection with the receiving platform.
The "Result Types" section will elaborate on the failed Section 4.3, "Result Types", will elaborate on the failed
negotiation attempts. This field contains an aggregate count of negotiation attempts. This field contains an aggregate count of
failed connections. failed connections.
4.3. Result Types 4.3. Result Types
The list of result types will start with the minimal set below, and The list of result types will start with the minimal set below, and
is expected to grow over time based on real-world experience. The is expected to grow over time based on real-world experience. The
initial set is: initial set is:
4.3.1. Negotiation Failures 4.3.1. Negotiation Failures
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chances of acceptance of the report at some compute cost. chances of acceptance of the report at some compute cost.
5.3. Email Transport 5.3. Email Transport
The report MAY be delivered by email. No specific MIME message The report MAY be delivered by email. No specific MIME message
structure is required. It is presumed that the aggregate reporting structure is required. It is presumed that the aggregate reporting
address will be equipped to extract MIME parts with the prescribed address will be equipped to extract MIME parts with the prescribed
media type and filename and ignore the rest. media type and filename and ignore the rest.
If compressed, the report should use the media type "application/ If compressed, the report should use the media type "application/
gzip" if compressed (see [RFC6713]), and "text/json" otherwise. gzip" if compressed (see [RFC6713]), and "application/json"
otherwise.
The [RFC5322].Subject field for individual report submissions SHOULD The [RFC5322].Subject field for individual report submissions SHOULD
conform to the following ABNF: conform to the following ABNF:
tlsrpt-subject = %x52.65.70.6f.72.74 1*FWS ; "Report" tlsrpt-subject = %x52.65.70.6f.72.74 1*FWS ; "Report"
%x44.6f.6d.61.69.6e.3a 1*FWS ; "Domain:" %x44.6f.6d.61.69.6e.3a 1*FWS ; "Domain:"
domain-name 1*FWS ; from RFC 6376 domain-name 1*FWS ; from RFC 6376
%x53.75.62.6d.69.74.74.65.72.3a ; "Submitter:" %x53.75.62.6d.69.74.74.65.72.3a ; "Submitter:"
1*FWS domain-name 1*FWS 1*FWS domain-name 1*FWS
%x52.65.70.6f.72.74.2d.49.44.3a ; "Report-ID:" %x52.65.70.6f.72.74.2d.49.44.3a ; "Report-ID:"
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Submitter: mail.sender.example.com Submitter: mail.sender.example.com
Report-ID: <735ff.e317+bf22029@mailexample.net> Report-ID: <735ff.e317+bf22029@mailexample.net>
Note that, when sending failure reports via SMTP, sending MTAs MUST Note that, when sending failure reports via SMTP, sending MTAs MUST
NOT honor MTA-STS or DANE TLSA failures. NOT honor MTA-STS or DANE TLSA failures.
5.4. HTTPS Transport 5.4. HTTPS Transport
The report MAY be delivered by POST to HTTPS. If compressed, the The report MAY be delivered by POST to HTTPS. If compressed, the
report should use the media type "application/gzip" (see [RFC6713]), report should use the media type "application/gzip" (see [RFC6713]),
and "text/json" otherwise. and "application/json" otherwise.
5.5. Delivery Retry 5.5. Delivery Retry
In the event of a delivery failure, regardless of the delivery In the event of a delivery failure, regardless of the delivery
method, a sender SHOULD attempt redelivery for up to 24hrs after the method, a sender SHOULD attempt redelivery for up to 24hrs after the
initial attempt. As previously stated the reports are optional, so initial attempt. As previously stated the reports are optional, so
while it is ideal to attempt redelivery, it is not required. If while it is ideal to attempt redelivery, it is not required. If
multiple retries are attempted, they should be on a logarithmic multiple retries are attempted, they should be on a logarithmic
scale. scale.
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o "report-id": A unique identifier for the report. Report authors o "report-id": A unique identifier for the report. Report authors
may use whatever scheme they prefer to generate a unique may use whatever scheme they prefer to generate a unique
identifier. It is provided as a string. identifier. It is provided as a string.
o "policy-type": The type of policy that was applied by the sending o "policy-type": The type of policy that was applied by the sending
domain. Presently, the only three valid choices are "tlsa", domain. Presently, the only three valid choices are "tlsa",
"sts", and the literal string "no-policy-found". It is provided "sts", and the literal string "no-policy-found". It is provided
as a string. as a string.
o "policy-string": The string serialization of the policy, whether o "policy-string": The JSON string serialization ([RFC7159] section
TLSA record or MTA-STS policy. Any linefeeds from the original 7) of the policy, whether TLSA record ([RFC6698] section 2.3) or
policy MUST be replaced with [SP]. TODO: Help with specifics. MTA-STS policy.
o "domain": The Policy Domain upon which the policy was applied. o "domain": The Policy Domain is the domain against which the MTA-
For messages sent to "user@example.com" this field would contain STS or DANE policy is defined.
"example.com". It is provided as a string.
o "mx-host-pattern": The pattern of MX hostnames from the applied o "mx-host-pattern": The pattern of MX hostnames from the applied
policy. It is provided as a string, and is interpreted in the policy. It is provided as a string, and is interpreted in the
same manner as the "Checking of Wildcard Certificates" rules in same manner as the "Checking of Wildcard Certificates" rules in
Section 6.4.3 of [RFC6125]. Section 6.4.3 of [RFC6125].
o "result-type": A value from the _Result Types_ section above. o "result-type": A value from Section 4.3, "Result Types", above.
o "ip-address": The IP address of the sending MTA that attempted the o "ip-address": The IP address of the sending MTA that attempted the
STARTTLS connection. It is provided as a string representation of STARTTLS connection. It is provided as a string representation of
an IPv4 or IPv6 address in dot-decimal or colon-hexadecimal an IPv4 or IPv6 address in dot-decimal or colon-hexadecimal
notation. notation.
o "receiving-mx-hostname": The hostname of the receiving MTA MX o "receiving-mx-hostname": The hostname of the receiving MTA MX
record with which the sending MTA attempted to negotiate a record with which the sending MTA attempted to negotiate a
STARTTLS connection. STARTTLS connection.
o "receiving-mx-helo": (optional) The HELO or EHLO string from the o "receiving-mx-helo": (optional) The HELO or EHLO string from the
banner announced during the reported session. banner announced during the reported session.
o "success-aggregate": The aggregate number (integer) of o "success-aggregate": The aggregate number (integer) of
successfully negotiated SSL-enabled connections to the receiving successfully negotiated TLS-enabled connections to the receiving
site. site.
o "failure-aggregate": The aggregate number (integer) of failures to o "failure-aggregate": The aggregate number (integer) of failures to
negotiate an SSL-enabled connection to the receiving site. negotiate an TLS-enabled connection to the receiving site.
o "session-count": The number of (attempted) sessions that match the o "session-count": The number of (attempted) sessions that match the
relevant "result-type" for this section. relevant "result-type" for this section.
o "additional-info-uri": An optional URI pointing to additional o "additional-info-uri": An optional URI pointing to additional
information around the relevant "result-type". For example, this information around the relevant "result-type". For example, this
URI might host the complete certificate chain presented during an URI might host the complete certificate chain presented during an
attempted STARTTLS session. attempted STARTTLS session.
o "failure-reason-code": A text field to include an SSL-related o "failure-reason-code": A text field to include an TLS-related
error code or error message. error code or error message.
10. Appendix 3: Example JSON Report 10. Appendix 3: Example JSON Report
{ {
"organization-name": "Company-X", "organization-name": "Company-X",
"date-range": { "date-range": {
"start-datetime": "2016-04-01T00:00:00Z", "start-datetime": "2016-04-01T00:00:00Z",
"end-datetime": "2016-04-01T23:59:59Z" "end-datetime": "2016-04-01T23:59:59Z"
}, },
"contact-info": "sts-reporting@company-x.com", "contact-info": "sts-reporting@company-x.com",
"report-id": "5065427c-23d3-47ca-b6e0-946ea0e8c4be", "report-id": "5065427c-23d3-47ca-b6e0-946ea0e8c4be",
"policy": { "policy": {
"policy-type": "sts", "policy-type": "sts",
skipping to change at page 16, line 33 skipping to change at page 16, line 33
[RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax [RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234, DOI 10.17487/ Specifications: ABNF", STD 68, RFC 5234, DOI 10.17487/
RFC5234, January 2008, RFC5234, January 2008,
<http://www.rfc-editor.org/info/rfc5234>. <http://www.rfc-editor.org/info/rfc5234>.
[RFC5322] Resnick, P., Ed., "Internet Message Format", RFC 5322, DOI [RFC5322] Resnick, P., Ed., "Internet Message Format", RFC 5322, DOI
10.17487/RFC5322, October 2008, 10.17487/RFC5322, October 2008,
<http://www.rfc-editor.org/info/rfc5322>. <http://www.rfc-editor.org/info/rfc5322>.
[RFC6068] Duerst, M., Masinter, L., and J. Zawinski, "The 'mailto'
URI Scheme", RFC 6068, DOI 10.17487/RFC6068, October 2010,
<http://www.rfc-editor.org/info/rfc6068>.
[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, <http://www.rfc-editor.org/info/rfc6125>. 2011, <http://www.rfc-editor.org/info/rfc6125>.
[RFC6698] Hoffman, P. and J. Schlyter, "The DNS-Based Authentication [RFC6698] Hoffman, P. and J. Schlyter, "The DNS-Based Authentication
of Named Entities (DANE) Transport Layer Security (TLS) of Named Entities (DANE) Transport Layer Security (TLS)
Protocol: TLSA", RFC 6698, DOI 10.17487/RFC6698, August Protocol: TLSA", RFC 6698, DOI 10.17487/RFC6698, August
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