...with most of the proposed changes to date, including Tony's (old)
proposed re-vamp of the ABNF for the header itself and correspondingly
adjusted examples.
Once we're approaching consensus, I'd like to submit this to the IETF to
replace the one that's up there (although then I'll also have to post
updates of all of our filters that use the header soon thereafter). I
definitely want to do that sometime this month so that things are
reasonably static by the time we head to Chicago.
Comments welcome.
-MSK
Individual submission M. Kucherawy
Internet-Draft Sendmail, Inc.
Intended status: Standards Track May 31, 2007
Expires: December 2, 2007
Message Header for Indicating Sender Authentication Status
draft-kucherawy-sender-auth-header-05
Status of this Memo
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Copyright Notice
Copyright (C) The IETF Trust (2007).
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Abstract
This memo defines a new message header for use with electronic mail
messages to indicate the results of sender authentication efforts.
Mail user agents (MUAs) may use this message header to relay that
information in a convenient way to users or to make sorting and
filtering decisions.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Purpose . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.2. Requirements . . . . . . . . . . . . . . . . . . . . . . . 4
1.3. Definitions . . . . . . . . . . . . . . . . . . . . . . . 4
2. Definition and Format of the Header . . . . . . . . . . . . . 6
2.1. General Description . . . . . . . . . . . . . . . . . . . 6
2.2. Formal Definition . . . . . . . . . . . . . . . . . . . . 6
2.3. Authentication Identifier Fields . . . . . . . . . . . . . 8
2.4. Result Values . . . . . . . . . . . . . . . . . . . . . . 9
2.5. Definition Of Initial Methods . . . . . . . . . . . . . . 9
2.6. Extension Fields . . . . . . . . . . . . . . . . . . . . . 10
3. Adding The Header To A Message . . . . . . . . . . . . . . . . 11
3.1. Header Position and Interpretation . . . . . . . . . . . . 11
4. Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . 13
4.1. Removing The Header . . . . . . . . . . . . . . . . . . . 13
5. Conformance and Usage Requirements . . . . . . . . . . . . . . 14
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
6.1. The Authentication-Results: header . . . . . . . . . . . . 15
6.2. Method Registry . . . . . . . . . . . . . . . . . . . . . 15
7. Security Considerations . . . . . . . . . . . . . . . . . . . 16
7.1. Non-conformant MTAs . . . . . . . . . . . . . . . . . . . 16
7.2. Header Position . . . . . . . . . . . . . . . . . . . . . 16
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 17
8.1. Normative References . . . . . . . . . . . . . . . . . . . 17
8.2. Informative References . . . . . . . . . . . . . . . . . . 17
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 18
Appendix B. Public Discussion . . . . . . . . . . . . . . . . . . 19
Appendix C. Legacy MUAs . . . . . . . . . . . . . . . . . . . . . 20
Appendix D. Authentication-Results Examples . . . . . . . . . . . 21
D.1. Trivial case; header not present . . . . . . . . . . . . . 21
D.2. Nearly-trivial case; service provided, but no
authentication done . . . . . . . . . . . . . . . . . . . 22
D.3. Service provided, authentication done . . . . . . . . . . 22
D.4. Service provided, several authentications done, single
MTA . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
D.5. Service provided, several authentications done,
different MTAs . . . . . . . . . . . . . . . . . . . . . . 24
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Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 26
Intellectual Property and Copyright Statements . . . . . . . . . . 27
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1. Introduction
This memo defines a new message header for electronic mail messages
which presents the results of a sender authentication effort in a
machine-readable format. The intent is to create a place to collect
such data when sender authentication mechanisms are in use so that an
MUA can provide a recommendation to the user as to the
trustworthiness of the message's origin and content.
This memo defines both the format of this new header, and discusses
the implications of its presence or absence.
[UPDATE PRIOR TO FINAL VERSION] At the time of publication of this
draft, [AUTH], [DOMAINKEYS], [DKIM], [SENDERID] and [SPF] are the
published e-mail authentication methods in common use. As various
methods emerge, it is necessary to prepare for their appearance and
encourage convergence in the area of interfacing these filters to
MUAs.
1.1. Purpose
The header defined in this memo is expected to serve several
purposes:
1. Convey to MUAs from filters and MTAs the results of various
sender authentication checks being applied;
2. Provide a common location for the presentation of this data;
3. Create an extensible framework for specifying new authentication
methods as such emerge;
4. Convey the results of sender authentication tests to later
filtering agents within the same "trust domain", as such agents
might apply more or less stringent checks based on sender
authentication results.
1.2. Requirements
This memo establishes no new requirements on existing protocols or
servers, as there is currently no standard place for the described
data to be collected or presented.
1.3. Definitions
This document occasionally uses terms that appear in capital letters.
When the terms "MUST", "SHOULD", "RECOMMENDED", "MUST NOT", "SHOULD
NOT", and "MAY" appear capitalized, they are being used to indicate
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particular requirements of this specification. A discussion of the
meanings of these terms appears in RFC2119.
Generally it is assumed that the work of applying sender
authentication schemes takes place at a border MTA, that is, an MTA
which acts as a gateway between the general Internet and the users
within an organizational boundary. This specification is written
with that assumption in mind. However, there are some sites at which
the entire mail infrastructure consists of a single host. In such
cases, such terms as "border MTA" and "delivery MTA" may well apply
to the same machine or even the very same agent.
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2. Definition and Format of the Header
This section gives a general overview of the format of the header
being defined, and then provides more formal specification.
2.1. General Description
The new header being defined here is called "Authentication-Results".
It is a Structured Header Field as defined in [MAIL] and thus all of
the related definitions in that document apply.
This new header MUST be added at the top of the message as it
transits MTAs which do authentication checks so some idea of how far
away the checks were done can be inferred. It therefore should be
treated as a Trace Header Field as defined in [MAIL] and thus all of
the related definitions in that document apply.
The decommented value of the header consists of an authentication
identifier, some whitespace, a "property=value" statement indicating
which property was selected to determine who sent the message and
what value was extracted from that property, followed by zero or more
authentication method names and a result associated with each,
returned by the code that implements the method.
As it is currently a matter of some debate, the header MAY appear
more than once in a single message, or more than one result MAY be
represented in a single header, or a combination of these MAY be
applied.
2.2. Formal Definition
Formally, the header is specified as follows:
header = "Authentication-Results:" [CFWS] authres-id CFWS
*([CFWS] ";" methodspec propspec )
authres-id = dot-atom-text
; see below for a description of this element;
; "dot-atom-text" is defined in section 3.2.4 of [MAIL]
methodspec = [CFWS] method [CFWS] "=" [CFWS] result [CFWS]
; indicates which authentication method was evaluated
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propspec = ptype [CFWS] "." [CFWS] property [CFWS] "=" value
; an indication of which property of the message
; was evaluated by the authentication scheme being
; applied to yield the reported result
method = token [ "/" version ]
; a method indicates which method's result is
; is represented by "value", and is one of the methods
; explicitly defined as valid in this document
; or is an extension method as defined below
version = 1*( ALPHA / DIGIT ) 0*( "." 1*( ALPHA / DIGIT ) )
; indicates which version of the method was applied
result = "pass" / "fail" / "softfail" / "neutral" /
"temperror" / "permerror"
; an indication of the results of the attempt to
; authenticate the sender
ptype = "smtp" / "header" / "body" / "policy"
; indicates whether the property being evaluated was
; a parameter to an [SMTP] command, or was a value taken
; from a message header, or was some property of the
; message body, or some other property evaluated by
; the receiving MTA
property = token
; if "ptype" is "smtp", this indicates which [SMTP]
; command provided the value which was evaluated by the
; authentication scheme being applied; if "ptype" is
; "header", this indicates from which header the value
; being evaluated was extracted; if "ptype" is
; "body", this indicates the offset into the body at which
; content of interest was detected; if "ptype" is "policy"
; then this indicates the name of the policy which caused
; this header to be added (see below)
value = [CFWS] token [CFWS] / mailbox
; the value extracted from the message property defined
; by the "ptype.property" construction; if the value
; identifies a mailbox, then it is a "mailbox"
; as defined in section 3.4 of [MAIL];
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; "mailbox" allows CFWS
The "token" is as defined in Appendix A of [MIME].
See Section 2.3 for a description of the "authres-id" element.
The list of commands eligible for use with the "smtp" ptype can be
found in [SMTP] and subsequent amendments.
"CFWS" is as defined in section 3.2.3 of [MAIL].
The "ptype" and "property" values used by each authentication method
should be defined in the specification for that method (or its
amendments).
The "ptype" and "property" are case-insensitive.
A "ptype" of "policy" indicates a policy decision about the message
not specific to a property of the message that could be extracted.
For example, if a method would normally report a "ptype.property" of
"header.From" and no From: header was present, the method can use
"policy" to indicate that no conclusion about the authenticity of the
message could be reached.
If the parsed "ptype.property" construction clearly identifies a
mailbox (in particular, smtp.mail, smtp.rcpt, header.from,
header.sender), then the "value" MUST be a "mailbox". Other
properties (e.g. smtp.helo) may be evaluated, but the property MUST
still be expressed as a "token" for simplified parsing.
2.3. Authentication Identifier Fields
Every Authentication-Results header MUST have an authentication
identifier field ("authres-id" above) which is a single result
identifier. This is similar in syntax to a fully-qualified domain
name.
The authentication identifier field provides a unique identifier that
refers to the authenticating service within a given mail
administrative domain. The uniqueness of the identifier is
guaranteed by the mail administrative domain that generates it and
must pertain to exactly that one mail administrative domain. This
identifier is intended to be machine-readable and not necessarily
meaningful to users. MUAs may use this identifier to determine
whether or not the data contained in an Authentication-Results header
can be trusted.
The mail administrative domain's unique domain name MUST be used as
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the last portion of the identifier.
Examples of valid authentication identifiers are mail.example.org,
engineering.example.edu and ms1.newyork.example.com.
2.4. Result Values
The six possible values of the "result" are:
pass: The message passed the authentication tests. (This may
require accessing an authentication policy of some kind published
by the sending domain.)
hardfail: The message failed the authentication tests. (This may
require accessing an authentication policy of some kind published
by the sending domain.)
softfail: The authentication method has either an explicit
(published by the sending domain) or implicit policy, but the
policy being used doesn't require successful authentication of all
messages from that domain, and the message failed the
authentication tests.
neutral: The authentication method completed without errors, but was
unable to reach either a positive or negative result about the
message.
temperror: A temporary (recoverable) error occurred attempting to
authenticate the sender; either the process couldn't be completed
locally, or (for methods requiring a policy to be accessed) there
was a temporary failure retrieving the sending domain's policy. A
later retry may produce a more final result.
permerror: A permanent (unrecoverable) error occurred attempting to
authenticate the sender; either the process couldn't be completed
locally, or (for methods requiring a policy to be accessed) there
was a permanent failure retrieving the sending domain's policy. A
later retry is unlikely to yield a final result.
New methods not specified in this document MUST indicate which of
these should be returned when exceptions such as syntax errors are
detected.
2.5. Definition Of Initial Methods
As they are currently existing specifications for sender
authentication, it is appropriate to define an authentication method
identifier for each of [AUTH], [DOMAINKEYS], [DKIM], [SENDERID] and
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[SPF]. Therefore, the authentication method identifiers "auth",
"domainkeys", "dkim", "senderid" and "spf" respectively are hereby
defined for MTAs applying those specifications for e-mail sender
authentication. See Section 6 for details.
2.6. Extension Fields
Additional authentication method identifiers may be defined in the
future by later revisions or extensions to this specification.
Extension identifiers beginning with "x-" will never be defined as
standard fields; such names are reserved for experimental use.
Method identifiers NOT beginning with "x-" MUST be registered with
the Internet Assigned Numbers Authority (IANA) and published in an
RFC.
Extension identifiers may be defined for the following reasons:
1. To allow additional information from emergent authentication
systems to be communicated to MUAs. The names of such
identifiers should reflect the name of the method being defined,
but should not be needlessly long.
2. To allow the creation of "sub-identifiers" which indicate
different levels of authentication and differentiate between
their relative strengths, e.g. "auth1-weak" and "auth1-strong".
Authentication method implementors are encouraged to provide adequate
information, via [MAIL] comments if necessary, to allow an MUA
developer to understand or relay ancilliary details of authentication
results. For example, if it might be of interest to relay what data
was used to perform an evaluation, such information could be relayed
as a comment in the header, such as:
Authentication-Results: mx.example.com; foo=pass (2 of 3 tests OK)
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3. Adding The Header To A Message
This specification makes no attempt to evaluate the relative
strengths of various sender authentication methods that may become
available. As such, the order of the presented authentication
methods and results MUST NOT be used to determine the importance or
strength of any given method over another. Instead, the MUA must
interpret the result of each method based on its knowledge of what
that method evaluates.
The "method" MUST refer to an authentication method declared in this
memo, or in a subsequent one, or to an authentication method name
assigned by IANA.
An MTA compliant with this specification MUST add this header (after
performing one or more sender authentication tests) to indicate at
which host the test was done, which test got applied and what the
result was. If an MTA applies more than one such test, it MUST
either add this header once per test, or one header indicating all of
the results. An MTA MUST NOT add a result to an existing header.
For security reasons, a border MTA conforming to this specification
MUST delete any discovered instance of this header which claims to
have been added within its trust boundary. For example, a border MTA
for example.com receiving a message from outside of its mail domain
MUST delete any instance of this header bearing an authentication
identifier indicating the header was added within that domain prior
to adding its own headers. This applies in both directions so that
hosts outside the domain cannot claim results MUAs inside the domain
might trust. However, care must be taken not to remove headers added
on messages which remain entirely within the originator's trust
boundary (i.e. local-to-local mail).
An MTA MAY add this header containing only the authentication
identifier portion to indicate explicitly that no sender
authentication schemes were applied prior to delivery of this
message.
3.1. Header Position and Interpretation
In order to ensure non-ambiguous results and avoid the impact of
false headers, an MUA SHOULD NOT interpret this header unless
specifically instructed to do so by the user. That is, this should
not be "on by default". Naturally then, users would not activate
such a feature unless they are certain the header will be added by
the receiving MTA that accepts the mail which is ultimately read by
the MUA, and instances of the header added by foreign MTAs will be
removed before delivery.
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Furthermore, an MUA SHOULD NOT interpret this header unless the
hostname it bears appears to be one within its own trust domain as
configured by the user.
An MUA should not reveal these results to naive end users unless the
results are accompanied by, at a minimum, some associated reputation
data about the sender which was authenticated.
As stated in Section 2.1, this header field SHOULD be treated as
though it were a trace header field as defined in section 3.6 of
[MAIL], and hence SHOULD not be reordered and SHOULD be prepended to
the message, so that there is generally some indication upon delivery
of where in the chain of handling MTAs the sender authentcation was
done.
Further discussion of this can be found in the Security
Considerations section below.
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4. Discussion
This section discusses various implementation issues not specifically
related to security. Security issues are discussed in a later
section.
4.1. Removing The Header
As specified in Section 3, instances of this header added by outside
MTAs which appear to come from inside an MTA's trust boundary must be
removed. In the case of messages signed using [DKIM] or other
message signing methods which sign headers, this may invalidate one
or more signature on the message if they included the header to be
removed at the time of signing. This behaviour is desirable since
there's no value in validating the signature on a message with forged
headers. However, signing agents MAY elect to omit these headers
from signing to avoid this situation.
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5. Conformance and Usage Requirements
An MTA or gateway conforms to this specification if it applies one or
more sender authentication mechanisms and inserts a header
corresponding to this specification after doing so and prior to
delivery.
MTAs that are relaying mail rather than delivering it, i.e. are not
part of an intended recipient's trust boundary, MAY perform sender
authentication or even take actions based on the results found, but
SHOULD NOT add an "Authentication-Results" header if relaying rather
than rejecting or discarding at the gateway. Conversely, an MTA
doing local delivery and some form of sender authentication MUST add
this header prior to delivery the message in order to be compliant.
A minimal implementation which does at least one sender
authentication check will add the header defined by this memo prior
to invoking local delivery procedures.
This specification places no restrictions on the processing of the
header's contents by user agents or distribution lists. It is
presented to those packages solely for their own information.
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6. IANA Considerations
This specification introduces some new namespaces that will be
registered with IANA. In all cases, new entries are assigned only
for values that have been documented in a published RFC that has IETF
Consensus, per [IANA-CONSIDERATIONS].
6.1. The Authentication-Results: header
Per [IANA-HEADERS], the "Authentication-Results:" header field is
added to the IANA Permanent Message Header Field Registry. The
following is the registration template:
Header field name: Authentication-Results
Applicable protocol: mail ([RFC2822])
Status: Standard
Author/Change controller: IETF
Specification document(s): [TBD]
Related information:
Requesting review of any proposed changes and additions to
this field is recommended.
6.2. Method Registry
As stated above, names of sender authentication methods supported by
this specification must be registered with IANA, with the exception
of experimental names as described above.
Each method must register a name, the specification which defines it,
which "ptype" is appropriate for use with that method, and which
"property" should be reported by that method.
The initial set of entries in this registry is as follows:
+------------+---------+--------+----------------------------+
| Method | defined | ptype | property |
+------------+---------+--------+----------------------------+
| auth | RFC2554 | smtp | auth |
+------------+---------+--------+----------------------------+
| domainkeys | RFC4870 | header | From or Sender |
+------------+---------+--------+----------------------------+
| dkim | RFC4871 | header | value of signature "i" tag |
+------------+---------+--------+----------------------------+
| senderid | RFC4406 | header | name of header used by PRA |
+------------+---------+--------+----------------------------+
| spf | RFC4408 | smtp | from |
+------------+---------+--------+----------------------------+
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7. Security Considerations
The following security considerations apply when applying or
processing the "Authentication-Results" header:
7.1. Non-conformant MTAs
An MUA that is aware of this specification which accesses a mailbox
whose mail is handled by a non-conformant MTA is in a position to
make false conclusions based on forged headers. A malicious user or
agent could forge a header using the destination MX for a receiving
domain as the hostname token in the value of the header, and with the
rest of the value claim that the sender was properly authenticated.
The non-conformant MTA would fail to strip the forged header, and the
MUA could inappropriately trust it.
It is for this reason an MUA SHOULD NOT have processing of the
"Authentication-Results" header enabled by default; instead it must
be ignored, at least for the purposes of enacting filtering
decisions, unless specifically enabled by the user after verifying
that the MTA is compliant. It is acceptable to have an MUA aware of
this standard, but have an explicit list of hostnames whose
"Authentication-Results" headers are trustworthy, however this list
SHOULD initially be empty.
Proposed alternate solutions to this problem are nascent. Possibly
the simplest is a digital signature on the header which can be
verified by a posted public key. Another would be a means to
interrogate the MTA that added the header to see if it is actually
providing any sender authentication services and saw the message in
question, but this isn't especially palatable. In either case, a
method needs to exist to verify that the host which appears to have
added the header (a) actually did so, and (b) is legitimately adding
that header for this delivery.
7.2. Header Position
Despite the requirements of [MAIL], headers can sometimes be
reordered enroute by intermediate MTAs. The goal of requiring header
addition only at the top of a message is an acknowledgement that some
MTAs do reorder headers, but most do not. Thus, in the general case,
there will be some indication of which MTAs (if any) handled the
message after the addition of the header defined here.
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8. References
8.1. Normative References
[MAIL] Resnick, P., "Internet Message Format", RFC 2822,
April 2001.
[MIME] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part One: Format of Internet Message
Bodies", RFC 2045, November 1996.
8.2. Informative References
[AUTH] Myers, J., "SMTP Service Extension for Authentication",
RFC 2554, March 1999.
[DKIM] Allman, E., Callas, J., Delany, M., Libbey, M., Fenton,
J., and M. Thomas, "DomainKeys Identified Mail (DKIM)
Signatures", RFC 4817, May 2007.
[DOMAINKEYS]
Delany, M., "Domain-based Email Authentication Using
Public Keys Advertised in the DNS (DomainKeys)", RFC 4870,
May 2007.
[IANA-CONSIDERATIONS]
Alvestrand, H. and T. Narten, "Guidelines for Writing an
IANA Considerations Section in RFCs", RFC 2434,
October 1998.
[IANA-HEADERS]
Klyne, G., Nottingham, M., and J. Mogul, "Registration
Procedures for Message Header Fields", RFC 2434,
September 2004.
[SENDERID]
Lyon, J. and M. Wong, "Sender ID: Authenticating E-Mail",
RFC 4406, April 2006.
[SMTP] Klensin, J., "Simple Mail Transfer Protocol", RFC 2821,
April 2001.
[SPF] Wong, M. and W. Schlitt, "Sender Policy Framework (SPF)
for Authorizing Use of Domains in E-Mail, Version 1",
RFC 4408, April 2006.
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Appendix A. Acknowledgements
The author wishes to acknowledge the following for their review and
constructive criticism of this proposal: Tony Hansen of AT&T, Mark
Delany and Miles Libbey of Yahoo! Inc., Jim Fenton of Cisco, and
Eric Allman of Sendmail, Inc.
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Appendix B. Public Discussion
Public discussion of this proposed specification is handled via the
mail-vet-discuss(_at_)mipassoc(_dot_)org mailing list. The list is open.
Access to subscription forms and to list archives can be found at
http://mipassoc.org/mailman/listinfo/mail-vet-discuss.
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Appendix C. Legacy MUAs
Implementors of this proposal should be aware that many MUAs are
unlikely to be retrofit to support the new header and its semantics.
In the interests of convenience and quicker adaptation, a delivery
MTA might want to consider adding things that are processed by
existing MUAs as well as the header defined by this specification.
One suggestion is to include a Priority: header, on messages which
don't already have such a header, containing a value that reflects
the strength of the authentication that was accomplished, e.g. "low"
for weak or no authentication, "normal" or "high" for good
authentication.
Certainly some modern MUAs can filter based on the content of this
header, but as there is keen interest in having MUAs make some kind
of graphical representation of this header's meaning, other interim
means of doing so may be necessary while this proposal is adopted.
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Appendix D. Authentication-Results Examples
This section presents some examples of the use of this header to
indicate authentication results.
D.1. Trivial case; header not present
The trivial case:
From: sender(_at_)example(_dot_)com
Received: from mail-router.example.com
(mail-router.example.com [1.2.3.4])
by server.sendmail.com (8.11.6/8.11.6)
with ESMTP id g1G0r1kA003489;
Fri, Feb 15 2002 17:19:07 -0800
Date: Fri, Feb 15 2002 16:54:30 -0800
To: receiver(_at_)sendmail(_dot_)com
Message-Id: <12345(_dot_)abc(_at_)example(_dot_)com>
Subject: here's a sample
Hello! Goodbye!
Example 1: Trivial case
The "Authentication-Results" header is completely absent. The MUA
may make no conclusion about the validity of the message. This could
be the case because the sender authentication services were not
available at the time of delivery, or no service is provided, or the
MTA is not in compliance with this specification.
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D.2. Nearly-trivial case; service provided, but no authentication done
A message that was delivered by an MTA which conforms to this
standard but provides no actual sender authentication service:
Authentication-Results: mail-router.example.com
From: sender(_at_)example(_dot_)com
Received: from mail-router.example.com
(mail-router.example.com [1.2.3.4])
by server.sendmail.com (8.11.6/8.11.6)
with ESMTP id g1G0r1kA003489;
Fri, Feb 15 2002 17:19:07 -0800
Date: Fri, Feb 15 2002 16:54:30 -0800
To: receiver(_at_)sendmail(_dot_)com
Message-Id: <12345(_dot_)abc(_at_)example(_dot_)com>
Subject: here's a sample
Hello! Goodbye!
Example 2: Header present but no authentication done
The "Authentication-Results" header is present, indicating that the
delivering MTA (which is named in the value of the header) conforms
to this specification. The absence of any method and result tokens
indicates that no sender authentication was done.
D.3. Service provided, authentication done
A message that was delivered by an MTA which conforms to this
standard and applied some sender authentication:
Authentication-Results: mail-router.example.com;
auth=pass (cram-md5)
smtp(_dot_)auth=sender(_at_)example(_dot_)com
From: sender(_at_)example(_dot_)com
Received: from dialup-1-2-3-4.example-isp.com
(dialup-1-2-3-4.example-isp.com [1.2.3.4])
by mail-router.example.com (8.11.6/8.11.6)
with ESMTP id g1G0r1kA003489;
Fri, Feb 15 2002 17:19:07 -0800
Date: Fri, Feb 15 2002 16:54:30 -0800
To: receiver(_at_)sendmail(_dot_)com
Message-Id: <12345(_dot_)abc(_at_)example(_dot_)com>
Subject: here's a sample
Hello! Goodbye!
Example 3: Header reporting results
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The "Authentication-Results" header is present, indicating that the
delivering MTA (which is identified in the value of the header)
conforms to this specification. Furthermore, the sender
authenticated herself/himself to the MTA via a method specified in
[AUTH]. The actual method is identified in a header comment after
the method's result is indicated. The MUA could extract and relay
this extra information if desired.
D.4. Service provided, several authentications done, single MTA
A message that was relayed inbound via a single MTA which conforms to
this standard and applied two different sender authentication checks:
Authentication-Results: mail-router.example.com;
auth=pass (cram-md5)
smtp(_dot_)mail=sender(_at_)example(_dot_)com;
spf=pass smtp(_dot_)mail=sender(_at_)example(_dot_)com
Authentication-Results: mail-router.example.com;
sender-id=pass header(_dot_)from=sender(_at_)example(_dot_)com
From: sender(_at_)example(_dot_)com
Received: from mail-router.example.com
(mail-router.example.com [1.2.3.4])
by dialup-1-2-3-4.example-isp.com (8.11.6/8.11.6)
with ESMTP id g1G0r1kA003489;
Fri, Feb 15 2002 17:19:07 -0800
Date: Fri, Feb 15 2002 16:54:30 -0800
To: receiver(_at_)sendmail(_dot_)com
Message-Id: <12345(_dot_)abc(_at_)example(_dot_)com>
Subject: here's a sample
Hello! Goodbye!
Example 4: Headers reporting results from one MTA
The "Authentication-Results" header is present, indicating the
delivering MTA (which is identified in the value of the header)
conforms to this specification. Furthermore, the sender
authenticated herself/himself to the MTA via a method specified in
[AUTH], and both [SPF] and [SENDERID] checks were done and passed.
The MUA could extract and relay this extra information if desired.
Two "Authentication-Results" headers are not required since the same
host did all of the checking. The authenticating agent could have
consolidated all the results into one header.
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D.5. Service provided, several authentications done, different MTAs
A message that was relayed inbound by two different MTAs which
conform to this standard and applied multiple sender authentication
checks:
Authentication-Results: auth-checker.example.com;
sender-id=pass
header(_dot_)from=sender(_at_)example(_dot_)com;
dkim=pass (good signature)
header(_dot_)i=sender(_at_)example(_dot_)com
Received: from mail-router.example.com
(mail-router.example.com [10.11.12.13])
by auth-checker.example.com (8.11.6/8.11.6)
with ESMTP id i7PK0sH7021929;
Fri, Feb 15 2002 17:19:22 -0800
Authentication-Results: mail-router.example.com;
auth=pass (cram-md5)
smtp(_dot_)mail=sender(_at_)example(_dot_)com;
spf=fail smtp(_dot_)mail=sender(_at_)example(_dot_)com
Received: from dialup-1-2-3-4.example-isp.com
(dialup-1-2-3-4.example-isp.com [1.2.3.4])
by mail-router.example.com (8.11.6/8.11.6)
with ESMTP id g1G0r1kA003489;
Fri, Feb 15 2002 17:19:07 -0800
DKIM-Signature: a=rsa-sha1; s=gatsby; d=example.com;
c=simple; q=dns;
b=EToRSuvUfQVP3Bkz ... rTB0t0gYnBVCM=
From: sender(_at_)example(_dot_)com
Date: Fri, Feb 15 2002 16:54:30 -0800
To: receiver(_at_)sendmail(_dot_)com
Message-Id: <12345(_dot_)abc(_at_)example(_dot_)com>
Subject: here's a sample
Hello! Goodbye!
Example 5: Headers reporting results from multiple MTAs
The "Authentication-Results" header is present, indicating
conformance to this specification. It is present twice because two
different MTAs in the chain of delivery did authentication tests.
The first, "mail-router.example.com" reports that [AUTH] and [SPF]
were both used, and [AUTH] passed but [SPF] failed. In the [AUTH]
case, additional data is provided in the comment field, which the MUA
can choose to render if desired.
The second MTA, identifying itself as "auth-checker.example.com",
reports that it did a [SENDERID] test and a [DKIM] test, both of
which passed. Again, additional data about one of the tests is
provided as a comment, which the MUA may choose to render.
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Since different hosts did the two sets of authentication checks, the
headers cannot be consolidated in this example.
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Author's Address
Murray S. Kucherawy
Sendmail, Inc.
6425 Christie Ave., Suite 400
Emeryville, CA 94608
US
Phone: +1 510 594 5400
Email: msk+ietf(_at_)sendmail(_dot_)com
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Full Copyright Statement
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contained in BCP 78, and except as set forth therein, the authors
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Kucherawy Expires December 2, 2007 [Page 27]
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