DANE: fix TA-mode verify under GnuTLS. Bug 2311

[exim.git] / doc / doc-txt / experimental-spec.txt

diff --git a/doc/doc-txt/experimental-spec.txt b/doc/doc-txt/experimental-spec.txt
index 4be142e6675e9fb3100f111f4c9bfa85e56bd57f..0ad7f0de9a01f502fa49ff41072ed4c37e3a81ff 100644 (file)
--- a/doc/doc-txt/experimental-spec.txt
+++ b/doc/doc-txt/experimental-spec.txt
@@ -436,6 +436,7 @@ dmarc_tld_file      Defines the location of a text file of valid
                     during domain parsing. Maintained by Mozilla,
                     the most current version can be downloaded
                     from a link at http://publicsuffix.org/list/.
                     during domain parsing. Maintained by Mozilla,
                     the most current version can be downloaded
                     from a link at http://publicsuffix.org/list/.

+                    See also util/renew-opendmarc-tlds.sh script.

 
 Optional:
 dmarc_history_file  Defines the location of a file to log results
 
 Optional:
 dmarc_history_file  Defines the location of a file to log results


@@ -446,11 +447,19 @@ dmarc_history_file  Defines the location of a file to log results
                     directory of this file is writable by the user
                     exim runs as.
 
                     directory of this file is writable by the user
                     exim runs as.
 

-dmarc_forensic_sender The email address to use when sending a
+dmarc_forensic_sender Alternate email address to use when sending a

                     forensic report detailing alignment failures
                     if a sender domain's dmarc record specifies it
                     and you have configured Exim to send them.
                     forensic report detailing alignment failures
                     if a sender domain's dmarc record specifies it
                     and you have configured Exim to send them.

-                    Default: do-not-reply@$default_hostname
+
+                   If set, this is expanded and used for the
+                   From: header line; the address is extracted
+                   from it and used for the envelope from.
+                   If not set, the From: header is expanded from
+                   the dsn_from option, and <> is used for the
+                   envelope from.
+
+                    Default: unset.

 
 
 3. By default, the DMARC processing will run for any remote,
 
 
 3. By default, the DMARC processing will run for any remote,


@@ -708,6 +717,8 @@ an external directory retaining the exim spool format.
 
 The spool files can then be processed by external processes and then
 requeued into exim spool directories for final delivery.
 
 The spool files can then be processed by external processes and then
 requeued into exim spool directories for final delivery.

+However, note carefully the warnings in the main documentation on
+qpool file formats.

 
 The motivation/inspiration for the transport is to allow external
 processes to access email queued by exim and have access to all the
 
 The motivation/inspiration for the transport is to allow external
 processes to access email queued by exim and have access to all the


@@ -792,34 +803,105 @@ standard header.
        Note that it would be wise to strip incoming messages of A-R headers
        that claim to be from our own <admd-identifier>.
 
        Note that it would be wise to strip incoming messages of A-R headers
        that claim to be from our own <admd-identifier>.
 

-There are two new variables: $arc_state and $arc_state_reason.
+There are three new variables: $arc_state, $arc_state_reason, $arc_domains:
+
+  $arc_state           One of pass, fail, none
+  $arc_state_reason    (if fail, why)
+  $arc_domains         colon-sep list of ARC chain domains, in chain order.
+                       problematic elements may have empty list elements
+  $arc_oldest_pass     lowest passing instance number of chain
+
+Example:
+  logwrite = oldest-p-ams: <${reduce {$lh_ARC-Authentication-Results:} \
+                               {} \
+                               {${if = {$arc_oldest_pass} \
+                                       {${extract {i}{${extract {1}{;}{$item}}}}} \
+                                       {$item} {$value}}} \
+                           }>

 
 Receive log lines for an ARC pass will be tagged "ARC".
 
 
 Signing
 --
 
 Receive log lines for an ARC pass will be tagged "ARC".
 
 
 Signing
 --

-arc_sign = <admd-identifier> : <selector> : <privkey>
+arc_sign = <admd-identifier> : <selector> : <privkey> [ : <options> ]

 An option on the smtp transport, which constructs and prepends to the message
 an ARC set of headers.  The textually-first Authentication-Results: header
 is used as a basis (you must have added one on entry to the ADMD).
 Expanded as a whole; if unset, empty or forced-failure then no signing is done.
 An option on the smtp transport, which constructs and prepends to the message
 an ARC set of headers.  The textually-first Authentication-Results: header
 is used as a basis (you must have added one on entry to the ADMD).
 Expanded as a whole; if unset, empty or forced-failure then no signing is done.

-If it is set, all three elements must be non-empty.
+If it is set, all of the first three elements must be non-empty.
+
+The fourth element is optional, and if present consists of a comma-separated list
+of options.  The options implemented are
+
+  timestamps           Add a t= tag to the generated AMS and AS headers, with the
+                       current time.
+  expire[=<val>]       Add an x= tag to the generated AMS header, with an expiry time.
+                       If the value <val> is an plain number it is used unchanged.
+                       If it starts with a '+' then the following number is added
+                       to the current time, as an offset in seconds.
+                       If a value is not given it defaults to a one month offset.
+
+[As of writing, gmail insist that a t= tag on the AS is mandatory]

 
 Caveats:
  * There must be an Authentication-Results header, presumably added by an ACL
    while receiving the message, for the same ADMD, for arc_sign to succeed.
    This requires careful coordination between inbound and outbound logic.
 
 Caveats:
  * There must be an Authentication-Results header, presumably added by an ACL
    while receiving the message, for the same ADMD, for arc_sign to succeed.
    This requires careful coordination between inbound and outbound logic.

+
+   Only one A-R header is taken account of.  This is a limitation versus
+   the ARC spec (which says that all A-R headers from within the ADMD must
+   be used).
+

  * If passing a message to another system, such as a mailing-list manager
    (MLM), between receipt and sending, be wary of manipulations to headers made
    by the MLM.
    + For instance, Mailman with REMOVE_DKIM_HEADERS==3 might improve
      deliverability in a pre-ARC world, but that option also renames the
      Authentication-Results header, which breaks signing.
  * If passing a message to another system, such as a mailing-list manager
    (MLM), between receipt and sending, be wary of manipulations to headers made
    by the MLM.
    + For instance, Mailman with REMOVE_DKIM_HEADERS==3 might improve
      deliverability in a pre-ARC world, but that option also renames the
      Authentication-Results header, which breaks signing.

+

  * Even if you use multiple DKIM keys for different domains, the ARC concept
    should try to stick to one ADMD, so pick a primary domain and use that for
    AR headers and outbound signing.
 
  * Even if you use multiple DKIM keys for different domains, the ARC concept
    should try to stick to one ADMD, so pick a primary domain and use that for
    AR headers and outbound signing.
 

+Signing is not compatible with cutthrough delivery; any (before expansion)
+value set for the option will result in cutthrough delivery not being
+used via the transport in question.
+
+
+
+
+REQUIRETLS support
+------------------
+Ref: https://tools.ietf.org/html/draft-ietf-uta-smtp-require-tls-03
+
+If compiled with EXPERIMENTAL_REQUIRETLS support is included for this
+feature, where a REQUIRETLS option is added to the MAIL command.
+The client may not retry in clear if the MAIL+REQUIRETLS fails (or was never
+offered), and the server accepts an obligation that any onward transmission
+by SMTP of the messages accepted will also use REQUIRETLS - or generate a
+fail DSN.
+
+The Exim implementation includes
+- a main-part option tls_advertise_requiretls; host list, default "*"
+- an observability variable $requiretls returning yes/no
+- an ACL "control = requiretls" modifier for setting the requirement
+- Log lines and Received: headers capitalise the S in the protocol
+  element: "P=esmtpS"
+
+Differences from spec:
+- we support upgrading the requirement for REQUIRETLS, including adding
+  it from cold, within an MTA.  The spec only define the sourcing MUA
+  as being able to source the requirement, and makes no mention of upgrade.
+- No support is coded for the RequireTLS header (which can be used
+  to annul DANE and/or STS policiy). [this can _almost_ be done in
+  transport option expansions, but not quite: it requires tha DANE-present
+  but STARTTLS-failing targets fallback to cleartext, which current DANE
+  coding specifically blocks]
+
+Note that REQUIRETLS is only advertised once a TLS connection is achieved
+(in contrast to STARTTLS).  If you want to check the advertising, do something
+like "swaks -s 127.0.0.1 -tls -q HELO".

 
 
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