On Feb 14, 2008, at 4:01 PM, Frank Ellermann wrote:
Douglas Otis wrote:
SMTP RFC2821
NNTP RFC3977
MSRP RFC4975
UUCP RFC976
Did you understand what I meant when I mentioned gateways ?
While this may not be a good initial list for transport protocols,
this was to illustrate more than one "public" transport is affected.
It would be incorrect to assume that a DKIM policy assertion applies
to all such transports. A receiver may not aggregate messages from
all transports into mailboxes primarily served by SMTP. Regardless of
the transport, DKIM might be used nonetheless. When a transmitting
domain has not implemented DKIM for a specific transport protocol,
then an assertion that "all" messages have been signed needs to
reflect where this has been implemented. Receivers will need to
decide whether they wish to merge the messages from one transport into
a mailbox served by SMTP. When the transport has been modified by an
up stream third-party, then receivers down stream are likely to apply
the policy pertinent to current transport. The syntax of the policy
record affords enough flexibility for the transmitter to express how
they wish to see policy applied.
As example, "s=SMTP:-UUCP:!*" would mean this domain only uses SMTP
and UUCP to exchange messages, but that this policy does not apply
to UUCP.
For a verifier at an MTA it is irrelevant how the message might have
started, if it arrives as "mail" (likely SMTP) it is "mail", and a
From header field is a From header field without studying the fine
print in RFC 4356, RFC.usefor-usefor, RFC 976, etc.
RFC 976 has status "unknown", this means MAJOR TROUBLE. I just read
John's appeal against the first RFC 4356 attempt again, it was a
disaster... <shudder />
Thanks for the input. It would seem this should be moved to an IANA
controlled protocol list.
policy-s-tag =
%x73 [FWS] "=" [FWS][exclude|disavow] policy-s-tag-type
No more [FWS] in SSP-02. it's now *WSP. It's now clear that net-
utf8 sticks to "disavow" HT, maybe SSP-03 should say *SP.
Sorry about that, was doing a quick cut and paste from the RFC 4871.
Take #3.
s= Policy Scope (plain-text; OPTIONAL; default is "*"). A colon-
separated list of policy scopes specify which protocols to which
this policy record applies. Verifiers for a given protocol MUST
ignore this record when the appropriate protocol has not been
listed. Currently defined protocol types are as follows:
* matches against all unlisted transport protocols
! disavows protocol use
- excludes protocol from policy assertions
SMTP RFC2821
NNTP RFC3977
See IANA SSP Policy List for additional protocols.
This tag is able to tailor the application of policy against
various transport protocols which may now or in the future
implement DKIM. This tag can also disavow use of specific
protocols to repudiate references to the domain.
A gateway that converts protocols ahead of the receiver may
change the policy applied. When uniform policy is desired for
all possible transports no tag is necessary, as the default is
"s=*". When a receiver combines messages from various
transports, it is RECOMMENDED the policy pertaining to the
primary transport protocol be applied. In most cases, this
policy would be for SMTP.
As example, "s=SMTP:-NNTP:!*" would mean this domain only uses
SMTP and NNTP to exchange messages, but that this policy does
not apply against NNTP. When a protocol has been disavowed,
any further DKIM related transactions should cease.
ABNF:
policy-s-tag = %x73 [WSP] "=" [WSP][exclude|disavow] policy-s-tag-
type
0*( [WSP] ":" [WSP] policy-s-tag-type )
disavow = "!"
exclude = "-"
policy-s-tag-type = "SMTP" /
"NNTP" /
"*" /
x-policy-s-tag-type
x-policy-s-tag-type = hyphenated-word ; for future extension
-Doug
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