draft-ietf-dkim-ssp-03.txt   draft-otis-dkim-adsp-02.txt 
Network Working Group E. Allman DKIM Working Group D. Otis
Internet-Draft Sendmail, Inc. Internet-Draft Trend Micro, NSSG
Intended status: Standards Track J. Fenton Intended status: Standards Track May 24, 2008
Expires: August 26, 2008 Cisco Systems, Inc. Expires: November 25, 2008
M. Delany
Yahoo! Inc.
J. Levine
Taughannock Networks
February 23, 2008
DKIM Author Signing Practices (ASP) DKIM Author Domain Signing Practices (ADSP)
draft-ietf-dkim-ssp-03 draft-otis-dkim-adsp-02
Status of this Memo Status of this Memo
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Copyright Notice Copyright Notice
Copyright (C) The IETF Trust (2008). Copyright (C) The IETF Trust (2008).
Abstract Abstract
DomainKeys Identified Mail (DKIM) defines a domain-level Author Domain Signing Practices (ADSP) advertises the adoption level
authentication framework for email using public-key cryptography and of DomainKeys Identified Mail (DKIM), as described in [RFC4871], for
key server technology to permit verification of the source and outbound messages publicly exchanged using SMTP, as described in
contents of messages by either Mail Transport Agents (MTAs) or Mail [RFC2821]. Application of ADSP by Mail User Agents (MUAs) might need
User Agents (MUAs). The primary DKIM protocol is described in to be offered as an option, to accommodate messages exchanged over
[RFC4871]. This document describes the records that authors' domains different public protocols. This document describes records that
can use to advertise their practices for signing their outgoing mail, authors' domains can publish to advertise their DKIM practices for
and how other hosts can access those records. outgoing messages containing the Author Domain. ADSP will not
dictate any specific use of DKIM identity parameters. Such identity
restrictions go beyond the charter and unnecessarily limit ADSP
applicability. Confirmation of an individual author's identity is
orthogonal to and fully independent of ADSP.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Language and Terminology . . . . . . . . . . . . . . . . . . . 4 2. Language and Terminology . . . . . . . . . . . . . . . . . . . 3
2.1. Terms Imported from DKIM Signatures Specification . . . . 4 2.1. Terms Imported from DKIM Signatures Specification . . . . 3
2.2. Valid Signature . . . . . . . . . . . . . . . . . . . . . 5 2.2. Valid Signature . . . . . . . . . . . . . . . . . . . . . 4
2.3. Author Address . . . . . . . . . . . . . . . . . . . . . . 5 2.3. Key Domain . . . . . . . . . . . . . . . . . . . . . . . . 4
2.4. Author Domain . . . . . . . . . . . . . . . . . . . . . . 5 2.4. Author Key Domain . . . . . . . . . . . . . . . . . . . . 4
2.5. Alleged Author . . . . . . . . . . . . . . . . . . . . . . 5 2.5. Author Address . . . . . . . . . . . . . . . . . . . . . . 4
2.6. Author Signing Practices . . . . . . . . . . . . . . . . . 5 2.6. Author Domain . . . . . . . . . . . . . . . . . . . . . . 4
2.7. Author Signature . . . . . . . . . . . . . . . . . . . . . 5 2.7. Author Domain Signing Practices . . . . . . . . . . . . . 4
3. Operation Overview . . . . . . . . . . . . . . . . . . . . . . 6 3. Operation Overview . . . . . . . . . . . . . . . . . . . . . . 4
3.1. ASP Usage . . . . . . . . . . . . . . . . . . . . . . . . 6 3.1. ADSP Usage . . . . . . . . . . . . . . . . . . . . . . . . 5
3.2. ASP Results . . . . . . . . . . . . . . . . . . . . . . . 6 3.2. ADSP Results . . . . . . . . . . . . . . . . . . . . . . . 5
4. Detailed Description . . . . . . . . . . . . . . . . . . . . . 7 4. Detailed Description . . . . . . . . . . . . . . . . . . . . . 5
4.1. DNS Representation . . . . . . . . . . . . . . . . . . . . 7 4.1. DNS Representation . . . . . . . . . . . . . . . . . . . . 5
4.2. Publication of ASP Records . . . . . . . . . . . . . . . . 7 4.2. Publication of ADSP Records . . . . . . . . . . . . . . . 6
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
5.1. ASP Specification Tag Registry . . . . . . . . . . . . . . 10 5.1. ADSP Specification Tag Registry . . . . . . . . . . . . . 9
5.2. ASP Outbound Signing Practices Registry . . . . . . . . . 10 5.2. ADSP Outbound Signing Practices Registry . . . . . . . . . 9
5.3. ASP Flags Registry . . . . . . . . . . . . . . . . . . . . 11 5.3. ADSP Flags Registry . . . . . . . . . . . . . . . . . . . 9
6. Security Considerations . . . . . . . . . . . . . . . . . . . 11 6. Security Considerations . . . . . . . . . . . . . . . . . . . 10
6.1. ASP Threat Model . . . . . . . . . . . . . . . . . . . . . 11 6.1. ADSP Threat Model . . . . . . . . . . . . . . . . . . . . 10
6.2. DNS Attacks . . . . . . . . . . . . . . . . . . . . . . . 12 6.2. DNS Attacks . . . . . . . . . . . . . . . . . . . . . . . 11
6.3. DNS Wildcards . . . . . . . . . . . . . . . . . . . . . . 12 6.3. DNS Wildcards . . . . . . . . . . . . . . . . . . . . . . 11
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13 7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12
7.1. References - Normative . . . . . . . . . . . . . . . . . . 13 7.1. References - Normative . . . . . . . . . . . . . . . . . . 12
7.2. References - Informative . . . . . . . . . . . . . . . . . 13 7.2. References - Informative . . . . . . . . . . . . . . . . . 13
Appendix A. Usage Examples . . . . . . . . . . . . . . . . . . . 13 Appendix A. Usage Examples . . . . . . . . . . . . . . . . . . . 13
A.1. Single Location Domains . . . . . . . . . . . . . . . . . 14 A.1. Single Location Domains . . . . . . . . . . . . . . . . . 13
A.2. Bulk Mailing Domains . . . . . . . . . . . . . . . . . . . 14 A.2. Bulk Mailing Domains . . . . . . . . . . . . . . . . . . . 13
A.3. Bulk Mailing Domains with Discardable Mail . . . . . . . . 14 A.3. Commonly Forged Transactional Messages . . . . . . . . . . 14
A.4. Third Party Senders . . . . . . . . . . . . . . . . . . . 15 A.4. Third Party Senders . . . . . . . . . . . . . . . . . . . 14
Appendix B. Acknowledgements . . . . . . . . . . . . . . . . . . 15 Appendix B. Acknowledgements . . . . . . . . . . . . . . . . . . 14
Appendix C. Change Log . . . . . . . . . . . . . . . . . . . . . 15 Appendix C. Changes in draft-otis-dkim-adsp-00 . . . . . . . . . 14
C.1. Changes since -ietf-dkim-02 . . . . . . . . . . . . . . . 15 Appendix D. Changes in draft-otis-dkim-adsp-01 . . . . . . . . . 15
C.2. Changes since -ietf-dkim-ssp-01 . . . . . . . . . . . . . 16 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 15
C.3. Changes since -ietf-dkim-ssp-00 . . . . . . . . . . . . . 17 Intellectual Property and Copyright Statements . . . . . . . . . . 16
C.4. Changes since -allman-ssp-02 . . . . . . . . . . . . . . . 17
C.5. Changes since -allman-ssp-01 . . . . . . . . . . . . . . . 18
C.6. Changes since -allman-ssp-00 . . . . . . . . . . . . . . . 18
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 18
Intellectual Property and Copyright Statements . . . . . . . . . . 20
1. Introduction 1. Introduction
DomainKeys Identified Mail (DKIM) defines a mechanism by which email DomainKeys Identified Mail (DKIM) defines a mechanism by which email
messages can be cryptographically signed, permitting a signing domain messages can be cryptographically signed, permitting a Key Domain to
to claim responsibility for the introduction of a message into the claim responsibility for the introduction of a message into the mail
mail stream. Message recipients can verify the signature by querying stream. Receiving hosts can verify the signature by querying the Key
the signer's domain directly to retrieve the appropriate public key, Domain to retrieve the appropriate public key, and thereby confirm
and thereby confirm that the message was attested to by a party in that the message was attested to by a party in possession of the
possession of the private key for the signing domain. private key and in control of a portion of the Key Domain.
However, the legacy of the Internet is such that not all messages However, the legacy of the Internet is such that not all messages
will be signed, and the absence of a signature on a message is not an will be signed, and the absence of a signature on a message is not an
a priori indication of forgery. In fact, during early phases of a priori indication of forgery. In fact, during early phases of
deployment it is very likely that most messages will remain unsigned. deployment it is likely that most messages will remain unsigned.
However, some domains might decide to sign all of their outgoing However, some domains might decide to sign all of their outgoing
mail, for example, to protect their brand name. It is desirable for mail, for example, to better protect their brand name. It is
such domains to be able to advertise that fact to other hosts. This desirable such domains be able to advertise that fact to other hosts.
is the topic of Author Signing Practices (ASP). This is the premise of Author Domain Signing Practices (ADSP).
Hosts implementing this specification can inquire what Author Signing Hosts implementing this specification can inquire what Author Domain
Practices a domain advertises. This inquiry is called an Author Signing Practices an Author Domain advertises. This inquiry is
Signing Practices check. called an Author Domain Signing Practices discovery.
The detailed requirements for Author Signing Practices are given in The detailed requirements for Author Domain Signing Practices are
[RFC5016]. This document refers extensively to [RFC4871] and assumes given in [RFC5016]. This document refers extensively to [RFC4871]
the reader is familiar with it. and assumes the reader is familiar with it.
Requirements Notation: The key words "MUST", "MUST NOT", "REQUIRED", Requirements Notation: The key words "MUST", "MUST NOT", "REQUIRED",
"SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED",
"MAY", and "OPTIONAL" in this document are to be interpreted as "MAY", and "OPTIONAL" in this document are to be interpreted as
described in [RFC2119] described in [RFC2119]
2. Language and Terminology 2. Language and Terminology
2.1. Terms Imported from DKIM Signatures Specification 2.1. Terms Imported from DKIM Signatures Specification
Some terminology used herein is derived directly from [RFC4871]. In Some terminology used herein is derived directly from [RFC4871]. In
several cases, references in that document to Sender have been several cases, references in that document to Sender have been
changed to Author here, to emphasize the relationship to the Author changed to Author here, to emphasize the relationship to the Author
address(es) in the From: header field described in [RFC2822]. address(es) in the From: header field described in [RFC2822].
Briefly, Briefly,
o A "Signer" is the agent that signs a message, as defined in
section 2.1 of [RFC4871].
o A "Selector" specifies which of the keys published by a signing
domain is to be queried, as defined in section 3.1 of [RFC4871].
o A "Local-part" is the part of an address preceding the @ sign, as o A "Local-part" is the part of an address preceding the @ sign, as
defined in [RFC2822] and used in [RFC4871]. defined in [RFC2822] and used in [RFC4871].
2.2. Valid Signature 2.2. Valid Signature
A "Valid Signature" is any signature on a message which correctly A "Valid Signature" is any message signature which correctly verifies
verifies using the procedure described in section 6.1 of [RFC4871]. using procedures described in section 6.1 of [RFC4871].
2.3. Author Address
An "Author Address" is an email address in the From header field of a 2.3. Key Domain
message [RFC2822]. If the From header field contains multiple
addresses, the message has multiple Author Addresses.
2.4. Author Domain The "Key Domain" is the domain listed in the "d=" tag of a Valid
Signature.
An "Author Domain" is everything to the right of the "@" in an Author 2.4. Author Key Domain
Address (excluding the "@" itself).
2.5. Alleged Author The "Author Key Domain" is the domain listed in the "d=" tag of a
Valid Signature that is at or above the Author Domain. The Author
Key Domain must match all of its domain components with that of the
Author Domain. When a referenced Key contains a "t=s" tag and value,
the Author Key Domain will match with the entire Author Domain. ADSP
does not require the "i=" tag to match with any local-parts, and can
include subdomains of the Author Domain.
An "Alleged Author" is an Author Address of a message; it is 2.5. Author Address
"alleged" because it has not yet been verified.
2.6. Author Signing Practices An "Author Address" is an email address in the From header field of a
message [RFC2822]. If the From header field contains multiple
addresses, the message has multiple Author Addresses.
"Author Signing Practices" (or just "practices") consist of a 2.6. Author Domain
machine-readable record published by the domain of an Alleged Author
which includes statements about the domain's practices with respect
to mail it sends with its domain in the From: line.
2.7. Author Signature An "Author Domain" is determined by the entire right-hand-side of the
Author Address (the portion that is to the right of the "@",
excluding the "@" itself).
An "Author Signature" is any Valid Signature where the identity of 2.7. Author Domain Signing Practices
the user or agent on behalf of which the message is signed (listed in
the ""i="" tag or its default value from the ""d="" tag) matches an
Author Address in the message. When the identity of the user or
agent includes a Local-part, the identities match if the Local-parts
match and the domains match. Otherwise, the identities match if the
domains match.
For example, if a message has a Valid Signature, with the DKIM- "Author Domain Signing Practices" (or just "practices") consist of a
Signature field containing "i=a@domain.example", then domain.example machine-readable record published at the "_adsp." subdomain of the
is asserting that it takes responsibility for the message. If the Author Domain. The ADSP record includes statements about the
message's From: field contains the address "b@domain.example" and an outgoing mail practices for messages containing the Author Domain.
ASP query produces a "dkim=all" or "dkim=discardable" result, that
would mean that the message does not have a valid Author Signature.
Even though the message is signed by the same domain, its failure to
satisfy ASP could be problematic.
3. Operation Overview 3. Operation Overview
Domain owners can publish Author Signing Practices via a query Domain owners can publish Author Domain Signing Practices via a
mechanism such as the Domain Name System; specific details are given distribution service, such as the Domain Name System; specific
in Section 4.1. details are given in Section 4.1.
Hosts can look up the Author Signing Practices of the domain(s) Hosts can obtain Author Domain Signing Practices of the domain(s)
specified by the Author Address(es) as described in Section 4.2.2. specified by the Author Domain as described in Section 4.2.2. If a
If a message has multiple Author Addresses the ASP lookups SHOULD be message has multiple Author Addresses, ADSP discoveries SHOULD be
performed independently on each address. This standard does not performed independently. This standard will not cover the
address the process a host might use to combine the lookup results. consolidation of combined ADSP results.
3.1. ASP Usage 3.1. ADSP Usage
Depending on the Author Domain(s) and the signatures in a message, a A receiving host might obtain varying amounts of useful information
recipient gets varying amounts of useful information from each ASP through ADSP transactions.
lookup.
o If a message has no Valid Signature, the ASP result is directly o If a message has no Valid Signature, ADSP results at the Author
relevant to the message. Domain are directly relevant to the message.
o If a message has a Valid Signature from an Author Domain, ASP o If a message has a Valid Signature from an Author Key Domain, ADSP
provides no benefit relative to that domain since the message is provides no benefit since the message is compliant with any
already known to be compliant with any possible ASP for that possible ADSP assertion.
domain.
o If a message has a Valid Signature from a domain other than an o If a message has a Valid Signature not at an Author Key Domain,
Author Domain, the receiver can use both the Signature and the ASP the receiver can use both the Key Domain and ADSP results in its
result in its evaluation of the message. evaluation of the message.
3.2. ASP Results 3.2. ADSP Results
An Author Signing Practices lookup for an Author Address produces one Author Domain Signing Practices discovery at an Author Domain
of four possible results: provides four possible results:
o Messages from this domain might or might not have an author o Messages containing the Author Domain may not have an Author Key
signature. This is the default if the domain exists in the DNS Domain signature.
but no record is found.
o All messages from this domain are signed. o All messages containing the Author Domain are initially signed by
an Author Key Domain.
o All messages from this domain are signed and discardable. o All messages containing the Author Domain not signed by an Author
Key Domain are to be dismissed.
o The domain does not exist. o The Author Domain can not support SMTP.
4. Detailed Description 4. Detailed Description
4.1. DNS Representation 4.1. DNS Representation
Author Signing Practices records are published using the DNS TXT Author Signing Practices records are published using the DNS TXT
resource record type. resource record type.
NON-NORMATIVE DISCUSSION [to be removed before publication]: There NON-NORMATIVE DISCUSSION [to be removed before publication]: There
has been considerable discussion on the DKIM WG mailing list has been considerable discussion on the DKIM WG mailing list
regarding the relative advantages of TXT and a new resource record regarding the relative advantages of TXT and a new resource record
(RR) type. Read the archive for details. (RR) type. Read the archive for details.
The RDATA for ASP resource records is textual in format, with The RDATA for ADSP resource records is textual in format, with
specific syntax and semantics relating to their role in describing specific syntax and semantics relating to their role in describing
Author Signing Practices. The "Tag=Value List" syntax described in Author Domain Signing Practices. The "Tag=Value List" syntax
section 3.2 of [RFC4871] is used. Records not in compliance with described in section 3.2 of [RFC4871] is used. Records not in
that syntax or the syntax of individual tags described in Section 4.3 compliance with that syntax or the syntax of individual tags
MUST be ignored (considered equivalent to a NODATA result) for described in Section 4.3 MUST be ignored, although they MAY cause the
purposes of ASP, although they MAY cause the logging of warning logging of warning messages via an appropriate system logging
messages via an appropriate system logging mechanism. If the RDATA mechanism. If the RDATA contains multiple character strings, the
contains multiple character strings, the strings are logically strings are to be logically concatenated with no delimiters placed
concatenated with no delimiters between the strings. between the strings.
The ASP record for a domain is published at a location in the
domain's DNS hierarchy prefixed by _asp._domainkey.; e.g., the ASP
record for example.com would be a TXT record that is published at
"_asp._domainkey.example.com". A domain MUST NOT publish more than
one ASP record; the semantics of an ASP lookup that returns multiple
ASP records for a single domain are undefined. (Note that
example.com and mail.example.com are different domains.)
4.2. Publication of ASP Records The ADSP record for an Author Domain is published at a "_adsp."
subdomain directly below the Author Domain; e.g., the ADSP record for
"example.com" would be a TXT record that is published at
"_adsp.example.com". A domain MUST NOT publish more than one ADSP
record; the semantics of an ADSP transaction returning multiple ADSP
records for a single domain are undefined. (Note that "example.com"
and "mail.example.com" are different domains.)
Author Signing Practices are intended to apply to all mail sent from 4.2. Publication of ADSP Records
the domain of an Alleged Author. In order to ensure that ASP applies
to any hosts within that domain (e.g., www.example.com,
ftp.example.com.) the ASP lookup algorithm looks up one level in the
domain tree. For example, mail signed by www.example.com could be
covered by the ASP record for example.com. This avoids the need to
include an ASP record for every name within a given domain.
Normally, a domain expressing Author Signing Practices will want to Author Domain Signing Practices are intended to apply to all mail
do so for both itself and all of its "descendants" (child domains at containing the Author Domain. As an optional defensive strategy
all lower levels). Domains wishing to do so MUST publish ASP records against subdomain spoofing, ADSP records could also be placed at
for the domain itself and any subdomains. domains that might appear to support SMTP.
Wildcards within a domain publishing ASP records pose a particular Wildcards within a domain publishing ADSP records will not pose a
problem. This is discussed in more detail in Section 6.3. problem. This is discussed in more detail in Section 6.3.
4.2.1. Record Syntax 4.2.1. Record Syntax
ASP records use the "tag=value" syntax described in section 3.2 of ADSP records use the "tag=value" syntax described in section 3.2 of
[RFC4871]. [RFC4871].
Tags used in ASP records are described below. Unrecognized tags MUST Tags used in ADSP records are described below. Unrecognized tags
be ignored. In the ABNF below, the WSP token is imported from MUST be ignored. In the ABNF below, the WSP token is imported from
[RFC2822]. The ALPHA and DIGIT tokens are imported from [RFC5234]. [RFC2822]. The ALPHA and DIGIT tokens are imported from [RFC5234].
dkim= Outbound signing practices for the domain (plain-text; dkim= practices (plain-text; REQUIRED). Possible values are as
REQUIRED). Possible values are as follows: follows:
unknown The domain might sign some or all email. OPEN (Default) The Author Domain permits unsigned outbound mail.
all All mail from the domain is signed with an Author Signature. CLOSED All mail containing the Author Domain is initially signed
by an Author Key Domain.
discardable All mail from the domain is signed with an Author LOCKED All mail containing the Author Domain is signed by an
Signature. Furthermore, if a message arrives without a valid Author Key Domain. Furthermore, if a message arrives without a
Author Signature due to modification in transit, submission via valid Author Key Domain signature, receiving hosts are
a path without access to a signing key, or other reason, the encouraged to dismiss the message.
domain encourages the recipient(s) to discard it.
ABNF: ABNF:
asp-dkim-tag = %x64.6b.69.6d *WSP "=" adsp-dkim-tag = %x64.6b.69.6d *WSP "="
*WSP ("unknown" / "all" / "discardable") *WSP ("OPEN" / "CLOSED" / "LOCKED")
t= Flags, represented as a colon-separated list of names (plain-text; t= Flags, represented as a colon-separated list of names (plain-text;
OPTIONAL, default is that no flags are set). Flag values are: OPTIONAL, default is that no flags are set). Flag values are:
s The signing practices apply only to the named domain, and not s The practices are not to be applied to subdomains of the Author
to subdomains. Domain. This information might assist receiving hosts to
better classify subdomains lacking MX or ADSP, but that have A
records during an MX mandate transitional phase.
ABNF: ABNF:
asp-t-tag = %x74 *WSP "=" *WSP { asp-t-tag-flag adsp-t-tag = %x74 *WSP "="
0*( *WSP ":" *WSP asp-t-tag-flag ) *WSP adsp-t-tag-flag 0*( *WSP ":" *WSP adsp-t-tag-flag )
asp-t-tag-flag = "s" / hyphenated-word
; for future extension adsp-t-tag-flag = "s" / hyphenated-word ; for future extension
hyphenated-word = ALPHA [ *(ALPHA / DIGIT / "-")
(ALPHA / DIGIT) ] hyphenated-word = ALPHA [ *(ALPHA / DIGIT / "-") (ALPHA / DIGIT) ]
Unrecognized flags MUST be ignored. Unrecognized flags MUST be ignored.
4.2.2. Author Signing Practices Lookup Procedure 4.2.2. Author Signing Practices Discovery Procedure
Hosts doing an ASP lookup MUST produce a result that is semantically Hosts discovering an ADSP record SHOULD produce a result semantically
equivalent to applying the following steps in the order listed below. equivalent to applying the following steps in the order listed below.
In practice, several of these steps can be performed in parallel in In practice, several of these steps can be performed in parallel to
order to improve performance. However, implementations SHOULD avoid improve performance. However, implementations SHOULD avoid
doing unnecessary DNS lookups. For the purposes of this section a unnecessary DNS transactions. For the purposes of this section a
"valid ASP record" is one that is both syntactically and semantically "valid ADSP record" is one that is both syntactically and
correct; in particular, it matches the ABNF for a "tag-list" and semantically correct; in particular, it matches the ABNF for a
includes a defined "dkim=" tag. "tag-list" and includes a defined "dkim=" tag.
1. _Fetch Named ASP Record._ The host MUST query DNS for a TXT 1. _Verify Domain Exists._ The host SHOULD perform a DNS query for
record corresponding to the Author Domain prefixed by an MX record at the Author Domain (with no prefix). If a non-
"_asp._domainkey." (note the trailing dot). If the result of existent domain error is returned, the discovery algorithm MUST
this query is a "NOERROR" response with an answer which is a terminate with an error indicating SMTP is not supported by the
valid ASP record, use that record; otherwise, continue to the Author Domain.
next step.
2. _Verify Domain Exists._ The host MUST perform a DNS query for a NON-NORMATIVE DISCUSSION: To better protect domains not
record corresponding to the Author Domain (with no prefix). The supporting SMTP, an initial query for an MX record is a
type of the query can be of any type, since this step is only to reasonable choice since this record is predominately published
determine if the domain itself exists in DNS. This query MAY be by domains supporting SMTP and is more readily cached than a
done in parallel with the query made in step 2. If the result of negative result. Whenever SMTP mandates MX records to support
this query is an "NXDOMAIN" error, the algorithm MUST terminate public exchanges, then not obtaining an MX record will
with an appropriate error. terminate the discovery algorithm with an appropriate error.
NON-NORMATIVE DISCUSSION: Any resource record type could be 2. _Fetch ADSP Record._ The host SHOULD query DNS for a TXT record
used for this query since the existence of a resource record corresponding to the Author Domain prefixed by "_adsp." (note the
of any type will prevent an "NXDOMAIN" error. MX is a trailing dot). If a valid ADSP record is obtained, use that
reasonable choice for this purpose is because this record type record; otherwise, continue to the next step.
is thought to be the most common for likely domains, and will
therefore result in a result which can be more readily cached
than a negative result.
3. _Try Parent Domain._ The host MUST query DNS for a TXT record for 3. _Verify Support of SMTP._ When an MX record has not been found at
the immediate parent domain, prefixed with "_asp._domainkey." If the Author Domain, the host SHOULD query DNS for an A record at
the result of this query is anything other than a "NOERROR" the Author Domain. When no A records exist at this location, the
response with a valid ASP record, the algorithm terminates with a discovery algorithm terminates with a result indicating SMTP is
result indicating that no ASP record was present. If the ASP "t" not supported by the Author Domain.
tag exists in the response and any of the flags is "s"
(indicating it does not apply to a subdomain), the algorithm also
terminates without finding an ASP record. Otherwise, use that
record.
If any of the queries involved in the Author Signing Practices Check NON-NORMATIVE DISCUSSION: Whenever SMTP mandates MX records to
result in a "SERVFAIL" error response, the algorithm terminates support public exchanges, subsequent checks for A records
without returning a result; possible actions include queuing the should not be made, since the discovery process would conclude
message or returning an SMTP error indicating a temporary failure. at the first step.
If any of the DNS transactions involved in Author Signing Practices
discovery result in a temporary error condition, the algorithm
terminates without returning a result; possible actions include
queuing the message or returning an SMTP error indicating a temporary
failure.
NOTE: Within a DNS transaction, as defined by [RFC1034] section
5.2.2 and [RFC4034] section 3, when a CNAME is returned, the alias
name is to be processed as if it were the initial name. [RFC2181]
section 10.3 makes an exception for Exchange host names returned
by MX records. An Exchange host name must not return a CNAME.
5. IANA Considerations 5. IANA Considerations
ASP introduces some new namespaces that have been registered with ADSP introduces some new namespaces that have been registered with
IANA. In all cases, new values are assigned only for values that IANA. In all cases, new values are assigned only for values that
have been documented in a published RFC that has IETF Consensus have been documented in a published RFC that has IETF Consensus
[RFC2434]. [RFC2434].
INFORMATIVE NOTE [ to be removed before publication ]: RFC 4871 INFORMATIVE NOTE [to be removed before publication]: Per the
defines a selector as a sub-domain, importing the term from RFC 2822. [RFC2822] definition, a domain must start with a letter or digit.
A sub-domain starts with a letter or digit, hence names such as _asp Hence names such as "_adsp." that start with an underscore cannot
that start with an underscore cannot collide with valid selectors. collide with host names and domains used by [RFC2821] and [RFC2822].
5.1. ASP Specification Tag Registry 5.1. ADSP Specification Tag Registry
An ASP record provides for a list of specification tags. IANA has An ADSP record provides for a list of specification tags. IANA has
established the ASP Specification Tag Registry for specification tags established the ADSP Specification Tag Registry for specification
that can be used in ASP fields. tags that can be used in ADSP fields.
The initial entries in the registry comprise: The initial entries in the registry comprise:
+------+-----------------+ +------+-----------------+
| TYPE | REFERENCE | | TYPE | REFERENCE |
+------+-----------------+ +------+-----------------+
| dkim | (this document) | | dkim | (this document) |
| t | (this document) | | t | (this document) |
+------+-----------------+ +------+-----------------+
ASP Specification Tag Registry Initial Values ADSP Specification Tag Registry Initial Values
5.2. ASP Outbound Signing Practices Registry 5.2. ADSP Outbound Signing Practices Registry
The "dkim=" tag spec, defined in Section 4.2.1, provides for a value The "dkim=" tag spec, defined in Section 4.2.1, provides for a value
specifying Outbound Signing Practices. IANA has established the ASP specifying Outbound Signing Practices. IANA has established the ADSP
Outbound Signing Practices Registry for Outbound Signing Practices. Outbound Signing Practices Registry for Outbound Signing Practices.
The initial entries in the registry comprise: The initial entries in the registry comprise:
+-------------+-----------------+ +-----------+-----------------+
| TYPE | REFERENCE | | TYPE | REFERENCE |
+-------------+-----------------+ +-----------+-----------------+
| unknown | (this document) | | OPEN | (this document) |
| all | (this document) | | CLOSED | (this document) |
| discardable | (this document) | | LOCKED | (this document) |
+-------------+-----------------+ +-----------+-----------------+
ASP Outbound Signing Practices Registry Initial Values ADSP Outbound Signing Practices Registry Initial Values
5.3. ASP Flags Registry 5.3. ADSP Flags Registry
The "t=" tag spec, defined in Section 4.2.1, provides for a value The "t=" tag spec, defined in Section 4.2.1, provides for a value
specifying Flags. IANA has established the ASP Flags Registry for specifying Flags. IANA has established the ADSP Flags Registry for
ASP Flags. ADSP Flags.
The initial entries in the registry comprise: The initial entries in the registry comprise:
+------+-----------------+ +------+-----------------+
| TYPE | REFERENCE | | TYPE | REFERENCE |
+------+-----------------+ +------+-----------------+
| s | (this document) | | s | (this document) |
+------+-----------------+ +------+-----------------+
ASP Flags Registry Initial Values ADSP Flags Registry Initial Values
6. Security Considerations 6. Security Considerations
Security considerations in the Author Signing Practices are mostly Security considerations in the Author Domain Signing Practices are
related to attempts on the part of malicious senders to represent mostly related to attempts on the part of malicious senders to
themselves as authors for whom they are not authorized to send mail, represent themselves as authors for whom they are not authorized to
often in an attempt to defraud either the recipient or an Alleged send mail, often in an attempt to defraud recipients of the message.
Author.
Additional security considerations regarding Author Signing Practices Messages signed by keys having a "g=" tag restricting the range of
are found in the DKIM threat analysis [RFC4686]. valid local-parts are likely applied by systems that are beyond the
direct control of the Author Key Domain. As a result, additional
care should be taken when the restricted local-part is not within an
Author Address. Acceptance of "g=" keys signing messages on behalf
of non-Author Addresses is discouraged.
6.1. ASP Threat Model Additional security considerations regarding Author Domain Signing
Practices are found in the DKIM threat analysis [RFC4686].
6.1. ADSP Threat Model
Email recipients often have a core set of content authors that they Email recipients often have a core set of content authors that they
already trust. Common examples include financial institutions with already trust. Common examples include financial institutions with
which they have an existing relationship and Internet web transaction which they have an existing relationship and Internet web transaction
sites with which they conduct business. sites with which they conduct business.
Email abuse often seeks to exploit the name-recognition that Email abuse often seeks to exploit the name-recognition that
recipients will have, for a legitimate email author, by using its recipients will have, for a legitimate email author, by using its
domain name in the From: header field. Especially since many popular domain name in the From: header field. Especially since many popular
MUAs do not display the author's email address, there is no empirical MUAs do not display the author's email address, there is no empirical
evidence of the extent that this particular unauthorized use of a evidence of the extent that this particular unauthorized use of a
domain name contributes to recipient deception or that eliminating it domain name contributes to recipient deception or that eliminating it
will have significant effect. will have significant effect.
However, closing this exploit could facilitate some types of However, closing this exploit could facilitate some types of
optimized processing by receive-side message filtering engines, since optimized processing by receive-side message filtering engines, since
it could permit them to maintain higher-confidence assertions about it could permit them to maintain higher-confidence assertions based
From: header field uses of a domain, when the occurrence is upon trusted Author Key Domains.
authorized.
Unauthorized uses of domain names occur elsewhere in messages, as do Unauthorized uses of domain names occur elsewhere in messages, as do
unauthorized uses of organizations' names. These attacks are outside unauthorized uses of organizations' names. These attacks are outside
the scope of this specification. the scope of this specification.
ASP does not provide any benefit--nor, indeed, have any effect at ADSP does not provide any benefit unless receiving host systems act
all--unless an external system acts upon the verdict, either by upon ADSP results, either by treating the message differently during
treating the message differently during the delivery process or by the delivery process or by showing some indicator to the end
showing some indicator to the end recipient. Such a system is out of recipient. Such a system is out of scope for this specification.
scope for this specification.
ASP Checkers perform up to three DNS lookups per Alleged Author The ADSP discovery algorithm performs up to three DNS transactions
Domain. Since these lookups are driven by domain names in email per Author Domain. Since these transactions are driven by domain
message headers of possibly fraudulent email, legitimate ASP Checkers names in email message headers of possibly fraudulent email,
can become participants in traffic multiplication attacks. receiving hosts attempting to discover ADSP records can become
participants in traffic multiplication attacks.
6.2. DNS Attacks 6.2. DNS Attacks
An attacker might attack the DNS infrastructure in an attempt to An attack might be waged against DNS infrastructure in an attempt to
impersonate ASP records, in an attempt to influence a receiver's disable services dependent upon DNS. Such attacks could be made
decision on how it will handle mail. However, such an attacker is worse by receiving hosts employing ADSP discovery. For this reason,
more likely to attack at a higher level, e.g., redirecting A or MX SMTP should consider making MX records mandatory for public
record lookups in order to capture traffic that was legitimately exchanges. The ADSP discovery process is not expected to impact the
intended for the target domain. These DNS security issues are likelihood of an attacker being successful at poisoning local DNS
addressed by DNSSEC [RFC4033]. resolvers. In addition, such DNS security issues are addressed by
DNSSEC [RFC4033].
Because ASP operates within the framework of the legacy e-mail Because ADSP operates within the framework of the legacy e-mail
system, the default result in the absence of an ASP record is that system, the default result in the absence of an ADSP record is for
the domain does not sign all of its messages. It is therefore the Author Domain to be considered "OPEN" where not all messages are
important that the ASP clients distinguish a DNS failure such as expected to be signed by a Author Key Domain. It is therefore
important that the ADSP clients distinguish a DNS failure such as
"SERVFAIL" from other DNS errors so that appropriate actions can be "SERVFAIL" from other DNS errors so that appropriate actions can be
taken. taken.
To ensure message reception remains viable for crucial systems when
DNS fails, IP addresses of crucial SMTP clients should be white
listed to allow ADSP and DKIM to be selectively bypassed during such
events.
6.3. DNS Wildcards 6.3. DNS Wildcards
Wildcards within a domain publishing ASP records, including but not Wildcards within a domain, excluding wildcard MX records, that also
limited to wildcard MX records, pose a particular problem. While publish ADSP records, do not pose a significant problem. While
referencing the immediate parent domain allows the discovery of an referencing SMTP related records will not provide "NXDOMAIN" results,
ASP record corresponding to an unintended immediate-child subdomain, either an MX or A record is still obtained as evidence of SMTP
wildcard records apply at multiple levels. For example, if there is support.
a wildcard MX record for "example.com", the domain
"foo.bar.example.com" can receive mail through the named mail
exchanger. Conversely, the existence of the record makes it
impossible to tell whether "foo.bar.example.com" is a legitimate name
since a query for that name will not return an "NXDOMAIN" error. For
that reason, ASP coverage for subdomains of domains containing a
wildcard record is incomplete.
NON-NORMATIVE NOTE: Complete ASP coverage of domains containing (or NON-NORMATIVE NOTE: Complete ADSP coverage for all subdomains of a
where any parent contains) wildcards generally cannot be provided by domain remains possible. However, ADSP records must be published at
standard DNS servers. every subdomain containing A records, in addition to subdomains
containing MX records. When SMTP adopts an MX record mandate for
public exchanges, ADSP records would be required only at subdomains
containing MX records.
7. References 7. References
7.1. References - Normative 7.1. References - Normative
[RFC1034] Mockapetris, P., "Domain names - concepts and facilities",
STD 13, RFC 1034, November 1987.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2181] Elz, R. and R. Bush, "Clarifications to the DNS
Specification", RFC 2181, July 1997.
[RFC2434] Narten, T. and H. Alvestrand, "Guidelines for Writing an [RFC2434] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 2434, IANA Considerations Section in RFCs", BCP 26, RFC 2434,
October 1998. October 1998.
[RFC2821] Klensin, J., "Simple Mail Transfer Protocol", RFC 2821,
April 2001.
[RFC2822] Resnick, P., "Internet Message Format", RFC 2822, [RFC2822] Resnick, P., "Internet Message Format", RFC 2822,
April 2001. April 2001.
[RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S. [RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "DNS Security Introduction and Requirements", Rose, "DNS Security Introduction and Requirements",
RFC 4033, March 2005. RFC 4033, March 2005.
[RFC4034] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "Resource Records for the DNS Security Extensions",
RFC 4034, March 2005.
[RFC4686] Fenton, J., "Analysis of Threats Motivating DomainKeys [RFC4686] Fenton, J., "Analysis of Threats Motivating DomainKeys
Identified Mail (DKIM)", RFC 4686, September 2006. Identified Mail (DKIM)", RFC 4686, September 2006.
[RFC4871] Allman, E., Callas, J., Delany, M., Libbey, M., Fenton, [RFC4871] Allman, E., Callas, J., Delany, M., Libbey, M., Fenton,
J., and M. Thomas, "DomainKeys Identified Mail (DKIM) J., and M. Thomas, "DomainKeys Identified Mail (DKIM)
Signatures", RFC 4871, May 2007. Signatures", RFC 4871, May 2007.
[RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax [RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234, January 2008. Specifications: ABNF", STD 68, RFC 5234, January 2008.
7.2. References - Informative 7.2. References - Informative
[RFC5016] Thomas, M., "Requirements for a DomainKeys Identified Mail [RFC5016] Thomas, M., "Requirements for a DomainKeys Identified Mail
(DKIM) Signing Practices Protocol", RFC 5016, (DKIM) Signing Practices Protocol", RFC 5016,
October 2007. October 2007.
Appendix A. Usage Examples Appendix A. Usage Examples
These examples are intended to illustrate typical uses of ASP. They These examples are intended to illustrate typical uses of ADSP. They
are not intended to be exhaustive, nor to apply to every domain's or are not intended to be exhaustive, nor to apply to every domain's or
mail system's individual situation. mail system's individual situation.
Domain managers are advised to consider the ways that mail processing Administrators are advised to consider the ways that mail processing
can modify messages in ways that will invalidate an existing DKIM can modify messages in a manner that will invalidate existing DKIM
signature, such as mailing lists, courtesy forwarders, and other signatures, such as mailing lists, courtesy forwarders, and other
paths that could add or modify headers, or modify the message body. paths that could add or modify headers, or modify the message body.
In that case, if the modifications invalidate the DKIM signature, In that case, if these modifications invalidate DKIM signatures,
recipient hosts will consider the mail not to have an Author receiving hosts will consider the mail not to have an Author Key
Signature, even though the signature was present when the mail was Domain signature, even though a Valid Signature was present when the
originally sent. mail was originally sent.
A.1. Single Location Domains A.1. Single Location Domains
A common mail system configuration handles all of a domain's users' A common mail system configuration handles all of a domain's users'
incoming and outgoing mail through a single MTA or group of MTAs. In incoming and outgoing mail through a single MTA or group of MTAs. In
that case, the MTA(s) can be configured to sign outgoing mail with an that case, the MTA(s) can be configured to sign outgoing mail with an
Author Signature. Author Key Domain signature.
In this situation it might be appropriate to publish an ASP record In this situation it might be appropriate to publish a "CLOSED" ADSP
for the domain containing "all", depending on whether the users also record for the Author Domain, depending on whether users also send
send mail through other paths that do not apply an Author Signature. mail through other paths that do not apply an Author Key Domain
Such paths could include MTAs at hotels or hotspot networks used by signature. Such paths could include MTAs at hotels or hotspot
travelling users, or web sites that provide "mail an article" networks used by travelling users, or web sites that provide "mail an
features. article" features.
A.2. Bulk Mailing Domains A.2. Bulk Mailing Domains
Another common configuration uses a domain solely for bulk or Another common configuration uses a domain solely for bulk or
broadcast mail, with no individual human users, again typically broadcast mail, with no individual human users, again typically
sending all the mail through a single MTA or group of MTAs that can sending all the mail through a single MTA or group of MTAs that can
apply an Author Signature. In this case, the domain's management can apply an Author Key Domain signature. In this case, before
be confident that all of its outgoing mail will be sent through the publishing a "CLOSED" ADSP record, the domain's management should be
signing MTA. Lacking individual users, the domain is unlikely to confident that all of its outgoing mail will be sent through signing
MTAs. Lacking individual users, the domain is unlikely to
participate in mailing lists, but could still send mail through other participate in mailing lists, but could still send mail through other
paths that might invalidate signatures. paths that might invalidate signatures.
Domain owners often use specialist mailing providers to send their Domain owners also often use specialist mailing providers to send
bulk mail. In that case, the mailing provider needs access to a their bulk mail. In that case, the mailing provider needs access to
suitable signing key in order to apply an Author Signature. One a suitable signing key in order to apply an Author Key Domain
possible route would be for the domain owner to generate the key and signature. One possible route would be for the Author Key Domain
give it to the mailing provider. Another would be for the domain to owner to generate the key and give it to the mailing provider.
delegate a subdomain to the mailing provider, for example, Another would be for the Author Key Domain to delegate a subdomain
bigbank.example might delegate email.bigbank.example to such a below the "_domainkey." label to the mailing provider. For example,
provider. In that case, the provider can generate the keys and DKIM "bigbank.example" might delegate "esp-00._domainkey.bigbank.example"
DNS records itself and use the subdomain in the Author address in the to such a provider. In that case, the provider could generate keys
mail. and DKIM DNS records itself and provide Author Key Domain signatures.
A.3. Bulk Mailing Domains with Discardable Mail A.3. Commonly Forged Transactional Messages
In some cases, a domain might sign all its outgoing mail with an In some cases, a domain might sign all its outgoing mail with an
Author Signature, but prefer that recipient systems discard mail Author Key Domain signature, but prefers that receiving host systems
without a valid Author Signature to avoid confusion from mail sent dismiss mail without a valid Author Key Domain signature to avoid
from sources that do not apply an Author Signature. (This latter confusion with mail sent from fraudulent sources unable to apply an
kind of mail is sometimes loosely called "forgeries".) In that case, Author Key Domain signature. (This latter kind of mail is sometimes
it might be appropriate to publish an ASP record containing loosely called "forgeries".) In that case, it might be appropriate
"discardable". Note that a domain SHOULD NOT publish a "discardable" to publish a "LOCKED" ADSP record. Note that a domain SHOULD NOT
record if it wishes to maximize the likelihood that mail from the publish a "LOCKED" ADSP record when it wishes to maximize the
domain is delivered, since it could cause some fraction of the mail likelihood that its mail is delivered, since it could cause some
the domain sends to be discarded. fraction of the mail to be discarded.
As a special case, if a domain sends no mail at all, it can safely As a special case, if a domain sends no mail at all, it can safely
publish a "discardable" ASP record, since any mail with an author publish a "LOCKED" ADSP record, since any mail with an Author Address
address in the domain is a forgery. for this domain is a forgery.
A.4. Third Party Senders A.4. Third Party Senders
Another common use case is for a third party to enter into an Another common use case is for a third party to enter into an
agreement whereby that third party will send bulk or other mail on agreement whereby that third party will send bulk or other mail on
behalf of a designated author domain, using that domain in the behalf of a designated Author Domain, using that domain in the
RFC2822 From: or other headers. Due to the many and varied RFC2822 From: or other headers. Due to the many and varied
complexities of such agreements, third party signing is not addressed complexities of such agreements, third party signing is not addressed
in this specification. in this specification.
Appendix B. Acknowledgements Appendix B. Acknowledgements
This document greatly benefited from comments by Steve Atkins, Jon This document was based upon the draft-ietf-dkim-ssp-003.
Callas, Dave Crocker, JD Falk, Arvel Hathcock, Ellen Siegel, Michael
Thomas, and Wietse Venema.
Appendix C. Change Log
*NOTE TO RFC EDITOR: This section may be removed upon publication of
this document as an RFC.*
C.1. Changes since -ietf-dkim-02
o Merge in more text from ASP draft.
o Phrase actions as host's rather than checker.
o Explanatory description of i= matching.
o Lookup procedure consistently refers to one ASP record per lookup.
o Update security section w/ language from W. Venema
o Simplify imports of terms from other RFCs, add Local-part, 4234 ->
5234.
o Add usage example appendix.
o Add IANA considerations.
o Update authors list
C.2. Changes since -ietf-dkim-ssp-01
o Reworded introduction for clarity.
o Various definition clarifications.
o Changed names of practices to unknown, all, and discardable.
o Removed normative language mandating use of SSP in particular
situations (issue 1538).
o Clarified possible confusion over handling of syntax errors.
o Removed normative language from Introduction (issue 1538).
o Changed "Originator" to "Author" throughout (issue 1529).
o Removed all references to Third-Party Signatures (issues 1512,
1521).
o Removed all mention of "Suspicious" (issues 1528, 1530).
o Removed "t=y" (testing) flag (issue 1540).
o Removed "handling" tag (issue 1513).
o Broke up the "Sender Signing Practices Check Procedure" into two
algorithms: fetching the SSP record and interpretation thereof
(issues 1531, 1535; partially addresses issue 1520).
Interpretation is now the responsibility of the Evaluator.
o Document restructuring for better flow and remove redundancies
(some may address issue 1523, but I'm not sure I understand that
issue completely; also issues 1532, 1537).
o Removed all mention of how this interacts with users, even though
it makes parts of the document harder to understand (issue 1526).
o Introduced the concepts of "SSP Checker" and "Evaluator".
o Multiple author case now handled my separate invocations of SSP
checker by Evaluator (issue 1525).
o Removed check to avoid querying top-level domains.
o Changed ABNF use of whitespace from [FWS] to *WSP (partially
addresses issue 1543).
C.3. Changes since -ietf-dkim-ssp-00
o Clarified Operation Overview and eliminated use of Legitimate as
the counterpart of Suspicious since the words have different
meanings.
o Improved discussion (courtesy of Arvel Hathcock) of the use of TXT
records in DNS vs. a new RR type.
o Clarified publication rules for multilevel names.
o Better description of overall record syntax, in particular that
records with unknown tags are considered syntactically correct.
o Clarified Sender Signing Practices Check Procedure, primarily by
use of new term Author Domain.
o Eliminated section "Third-Party Signatures and Mailing Lists" that
is better included in the DKIM overview document.
o Added "handling" tag to express alleged sending domain's
preference about handling of Suspicious messages.
o Clarified handling of SERVFAIL error in SSP check.
o Replaced "entity" with "domain", since with the removal of user-
granularity SSP, the only entities having sender signing policies
are domains.
C.4. Changes since -allman-ssp-02
o Removed user-granularity SSP and u= tag.
o Replaced DKIMP resource record with a TXT record.
o Changed name of the primary tag from "p" to "dkim".
o Replaced lookup algorithm with one which traverses upward at most
one level.
o Added description of records to be published, and effect of
wildcard records within the domain, on SSP.
C.5. Changes since -allman-ssp-01
o Changed term "Sender Signing Policy" to "Sender Signing
Practices".
o Changed query methodology to use a separate DNS resource record
type, DKIMP.
o Changed tag values from SPF-like symbols to words.
o User level policies now default to that of the domain if not
specified.
o Removed the "Compliance" section since we're still not clear on
what goes here.
o Changed the "parent domain" policy to only search up one level
(assumes that subdomains will publish SSP records if appropriate).
o Added detailed description of SSP check procedure.
C.6. Changes since -allman-ssp-00
From a "diff" perspective, the changes are extensive. Semantically,
the changes are:
o Added section on "Third-Party Signatures and Mailing Lists"
o Added "Compliance" (transferred from -base document). I'm not
clear on what needs to be done here.
o Extensive restructuring.
Authors' Addresses
Eric Allman Appendix C. Changes in draft-otis-dkim-adsp-00
Sendmail, Inc.
6475 Christie Ave, Suite 350
Emeryville, CA 94608
Phone: +1 510 594 5501 o Conditioned Author Signing Practices Discovery Procedure SMTP
Email: eric+dkim@sendmail.org verification step to be made only when an MX record had not been
Jim Fenton found.
Cisco Systems, Inc.
MS SJ-9/2
170 W. Tasman Drive
San Jose, CA 95134-1706
Phone: +1 408 526 5914 Appendix D. Changes in draft-otis-dkim-adsp-01
Email: fenton@cisco.com
Mark Delany o Modified the Author Signing Practices Discovery Procedure to
Yahoo! Inc. better conform with terms in RFC2821. In addition, a note now
701 First Avenue covers the issue of CNAMEs.
Sunnyvale, CA 94089
Phone: +1 408 349 6831 Author's Address
Email: markd+dkim@yahoo-inc.com
John Levine Douglas Otis
Taughannock Networks Trend Micro, NSSG
PO Box 727 10101 N. De Anza Blvd
Trumansburg, NY 14886 Cupertino, CA 95014
USA
Phone: +1 831 480 2300 Phone: +1.408.257-1500
Email: standards@taugh.com Email: doug_otis@trendmicro.com
URI: http://www.taugh.com
Full Copyright Statement Full Copyright Statement
Copyright (C) The IETF Trust (2008). Copyright (C) The IETF Trust (2008).
This document is subject to the rights, licenses and restrictions This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors contained in BCP 78, and except as set forth therein, the authors
retain all their rights. retain all their rights.
This document and the information contained herein are provided on an This document and the information contained herein are provided on an
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