As client, request PRDR by default if the server offers it

[users/jgh/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 28591eaf7085f5fc56d88c65d3beb516eba6540f..d57cbf9038a1373755c692ef33f4c40879f6b3f8 100644 (file)
--- a/doc/doc-txt/experimental-spec.txt
+++ b/doc/doc-txt/experimental-spec.txt
@@ -759,38 +759,46 @@ b. Configure, somewhere before the DATA ACL, the control option to
 
 
 
 
 
 

-Transport post-delivery actions
+Event Actions

 --------------------------------------------------------------
 
 --------------------------------------------------------------
 

-An arbitrary per-transport string can be expanded on successful delivery,
-and (for SMTP transports) a second string on deferrals caused by a host error.
+(Renamed from TPDA, Transport post-delivery actions)
+
+An arbitrary per-transport string can be expanded upon various transport events.
+Additionally a main-section configuration option can be expanded on some
+per-message events.

 This feature may be used, for example, to write exim internal log information
 (not available otherwise) into a database.
 
 In order to use the feature, you must compile with
 
 This feature may be used, for example, to write exim internal log information
 (not available otherwise) into a database.
 
 In order to use the feature, you must compile with
 

-EXPERIMENTAL_TPDA=yes
+EXPERIMENTAL_EVENT=yes

 
 in your Local/Makefile
 
 
 in your Local/Makefile
 

-and define the tpda_event_action option in the transport, to
-be expanded when the event fires.
+and define one or both of
+- the event_action option in the transport
+- the event_action main option
+to be expanded when the event fires.

 
 

-A new variable, $tpda_event, is set to the event type when the
+A new variable, $event_name, is set to the event type when the

 expansion is done.  The current list of events is:
 
 expansion is done.  The current list of events is:
 

-       msg:delivery
-       msg:host:defer
-       tcp:connect
-       tcp:close
-       tls:cert
-       smtp:connect
-
-The expansion is called for all event types, and should use the $tpda_event
+ msg:complete          after  main       per message
+ msg:delivery          after  transport  per recipient
+ msg:host:defer                after  transport  per attempt
+ msg:fail:delivery     after  main       per recipient
+ msg:fail:internal     after  main       per recipient
+ tcp:connect           before transport  per connection
+ tcp:close             after  transport  per connection
+ tls:cert              before both       per certificate in verification chain
+ smtp:connect          after  transport  per connection
+
+The expansion is called for all event types, and should use the $event_name

 value to decide when to act.  The variable data is a colon-separated
 list, describing an event tree.
 
 value to decide when to act.  The variable data is a colon-separated
 list, describing an event tree.
 

-There is an auxilary variable, $tpda_data, for which the
+There is an auxilary variable, $event_data, for which the

 content is event_dependent:
 
        msg:delivery            smtp confirmation mssage
 content is event_dependent:
 
        msg:delivery            smtp confirmation mssage


@@ -798,9 +806,9 @@ content is event_dependent:
        tls:cert                verification chain depth
        smtp:connect            smtp banner
 
        tls:cert                verification chain depth
        smtp:connect            smtp banner
 

-The msg:host:defer event populates one extra variable, $tpda_defer_errno.
+The msg:host:defer event populates one extra variable, $event_defer_errno.

 
 

-The following variables are likely to be useful for most event types:
+The following variables are likely to be useful depending on the event type:

 
        router_name, transport_name
        local_part, domain
 
        router_name, transport_name
        local_part, domain


@@ -808,11 +816,12 @@ The following variables are likely to be useful for most event types:
        tls_out_peercert
        lookup_dnssec_authenticated, tls_out_dane
        sending_ip_address, sending_port
        tls_out_peercert
        lookup_dnssec_authenticated, tls_out_dane
        sending_ip_address, sending_port

+       message_exim_id, verify_mode

 
 
 An example might look like:
 
 
 
 An example might look like:
 

-tpda_event_action = ${if = {msg:delivery}{$tpda_event} \
+event_action = ${if = {msg:delivery}{$event_name} \

 {${lookup pgsql {SELECT * FROM record_Delivery( \
     '${quote_pgsql:$sender_address_domain}',\
     '${quote_pgsql:${lc:$sender_address_local_part}}', \
 {${lookup pgsql {SELECT * FROM record_Delivery( \
     '${quote_pgsql:$sender_address_domain}',\
     '${quote_pgsql:${lc:$sender_address_local_part}}', \


@@ -823,27 +832,30 @@ tpda_event_action = ${if = {msg:delivery}{$tpda_event} \
     '${quote_pgsql:$message_exim_id}')}} \
 } {}}
 
     '${quote_pgsql:$message_exim_id}')}} \
 } {}}
 

-The string is expanded after the delivery completes and any
-side-effects will happen.  The result is then discarded.
+The string is expanded when each of the supported events occur
+and any side-effects of the expansion will happen.

 Note that for complex operations an ACL expansion can be used.
 
 Note that for complex operations an ACL expansion can be used.
 

-During the expansion the tpda_event variable will contain the
-string-list "msg:delivery".
-

 
 

-The expansion of the tpda_event_action option should normally
+The expansion of the event_action option should normally

 return an empty string.  Should it return anything else the
 following will be forced:
 
        msg:delivery    (ignored)
        msg:host:defer  (ignored)
 return an empty string.  Should it return anything else the
 following will be forced:
 
        msg:delivery    (ignored)
        msg:host:defer  (ignored)

+       msg:fail:delivery (ignored)

        tcp:connect     do not connect
        tcp:close       (ignored)
        tls:cert        refuse verification
        smtp:connect    close connection
 
        tcp:connect     do not connect
        tcp:close       (ignored)
        tls:cert        refuse verification
        smtp:connect    close connection
 

+No other use is made of the result string.

 
 
 
 

+Known issues:
+- the tls:cert event is only called for the cert chain elements
+  received over the wire, with GnuTLS.  OpenSSL gives the entire
+  chain including thse loaded locally.

 
 
 Redis Lookup
 
 
 Redis Lookup


@@ -1132,6 +1144,8 @@ the next hop does not support DSN.
 Adding it to a redirect router makes no difference.
 
 
 Adding it to a redirect router makes no difference.
 
 

+
+

 Certificate name checking
 --------------------------------------------------------------
 The X509 certificates used for TLS are supposed be verified
 Certificate name checking
 --------------------------------------------------------------
 The X509 certificates used for TLS are supposed be verified


@@ -1139,16 +1153,33 @@ that they are owned by the expected host.  The coding of TLS
 support to date has not made these checks.
 
 If built with EXPERIMENTAL_CERTNAMES defined, code is
 support to date has not made these checks.
 
 If built with EXPERIMENTAL_CERTNAMES defined, code is

-included to do so, and a new smtp transport option
-"tls_verify_cert_hostname" supported which takes a list of
-names for which the checks must be made.  The host must
-also be in "tls_verify_hosts".
+included to do so for server certificates, and a new smtp transport option
+"tls_verify_cert_hostnames" supported which takes a hostlist
+which must match the target host for the additional checks must be made.
+The option currently defaults to empty, but this may change in
+the future.  "*" is probably a suitable value.
+Whether certificate verification is done at all, and the result of
+it failing, is stll under the control of "tls_verify_hosts" nad
+"tls_try_verify_hosts".
+
+The name being checked is that for the host, generally
+the result of an MX lookup.

 
 Both Subject and Subject-Alternate-Name certificate fields
 are supported, as are wildcard certificates (limited to
 a single wildcard being the initial component of a 3-or-more
 component FQDN).
 
 
 Both Subject and Subject-Alternate-Name certificate fields
 are supported, as are wildcard certificates (limited to
 a single wildcard being the initial component of a 3-or-more
 component FQDN).
 

+The equivalent check on the server for client certificates is not
+implemented.  At least one major email provider is using a client
+certificate which fails this check.  They do not retry either without
+the client certificate or in clear.
+
+It is possible to duplicate the effect of this checking by
+creative use of Events.
+
+
+

 
 DANE
 ------------------------------------------------------------
 
 DANE
 ------------------------------------------------------------


@@ -1172,6 +1203,10 @@ admins of the target server.   The attack surface presented
 by (a) is thought to be smaller than that of the set
 of root CAs.
 
 by (a) is thought to be smaller than that of the set
 of root CAs.
 

+It also allows the server to declare (implicitly) that
+connections to it should use TLS.  An MITM could simply
+fail to pass on a server's STARTTLS.
+

 DANE scales better than having to maintain (and
 side-channel communicate) copies of server certificates
 for every possible target server.  It also scales
 DANE scales better than having to maintain (and
 side-channel communicate) copies of server certificates
 for every possible target server.  It also scales


@@ -1196,12 +1231,12 @@ There are no changes to Exim specific to server-side
 operation of DANE.
 
 The TLSA record for the server may have "certificate
 operation of DANE.
 
 The TLSA record for the server may have "certificate

-usage" of DANE_TA(2) or DANE_EE(3).  The latter specifies
+usage" of DANE-TA(2) or DANE-EE(3).  The latter specifies

 the End Entity directly, i.e. the certificate involved
 is that of the server (and should be the sole one transmitted
 during the TLS handshake); this is appropriate for a
 single system, using a self-signed certificate.
 the End Entity directly, i.e. the certificate involved
 is that of the server (and should be the sole one transmitted
 during the TLS handshake); this is appropriate for a
 single system, using a self-signed certificate.

-  DANE_TA usage is effectively declaring a specific CA
+  DANE-TA usage is effectively declaring a specific CA

 to be used; this might be a private CA or a public,
 well-known one.  A private CA at simplest is just
 a self-signed certificate which is used to sign
 to be used; this might be a private CA or a public,
 well-known one.  A private CA at simplest is just
 a self-signed certificate which is used to sign


@@ -1213,7 +1248,7 @@ the entire certificate chain from CA to server-certificate.
 If a public CA is used then all clients must be primed with it
 (losing one advantage of DANE) - but the attack surface is
 reduced from all public CAs to that single CA.
 If a public CA is used then all clients must be primed with it
 (losing one advantage of DANE) - but the attack surface is
 reduced from all public CAs to that single CA.

-DANE_TA is commonly used for several services and/or
+DANE-TA is commonly used for several services and/or

 servers, each having a TLSA query-domain CNAME record,
 all of which point to a single TLSA record.
 
 servers, each having a TLSA query-domain CNAME record,
 all of which point to a single TLSA record.
 


@@ -1230,13 +1265,13 @@ is useful for quickly generating TLSA records; and commands like
 
 are workable for 4th-field hashes.
 
 
 are workable for 4th-field hashes.
 

-For use with the DANE_TA model, server certificates
+For use with the DANE-TA model, server certificates

 must have a correct name (SubjectName or SubjectAltName).
 
 The use of OCSP-stapling should be considered, allowing
 for fast revocation of certificates (which would otherwise
 be limited by the DNS TTL on the TLSA records).  However,
 must have a correct name (SubjectName or SubjectAltName).
 
 The use of OCSP-stapling should be considered, allowing
 for fast revocation of certificates (which would otherwise
 be limited by the DNS TTL on the TLSA records).  However,

-this is likely to only be usable with DANE_TA.  NOTE: the
+this is likely to only be usable with DANE-TA.  NOTE: the

 default of requesting OCSP for all hosts is modified iff
 DANE is in use, to:
 
 default of requesting OCSP for all hosts is modified iff
 DANE is in use, to:
 


@@ -1247,13 +1282,15 @@ DANE is in use, to:
 The (new) variable $tls_out_tlsa_usage is a bitfield with
 numbered bits set for TLSA record usage codes.
 The zero above means DANE was not in use,
 The (new) variable $tls_out_tlsa_usage is a bitfield with
 numbered bits set for TLSA record usage codes.
 The zero above means DANE was not in use,

-the four means that only DANE_TA usage TLSA records were
-found. If the definition of hosts_require_ocsp or
-hosts_request_ocsp includes the string "tls_out_tlsa_usage",
-they are re-expanded in time to control the OCSP request.
+the four means that only DANE-TA usage TLSA records were
+found. If the definition of hosts_request_ocsp includes the
+string "tls_out_tlsa_usage", they are re-expanded in time to
+control the OCSP request.

 
 This modification of hosts_request_ocsp is only done if
 
 This modification of hosts_request_ocsp is only done if

-it has the default value of "*".
+it has the default value of "*".  Admins who change it, and
+those who use hosts_require_ocsp, should consider the interaction
+with DANE in their OCSP settings.

 
 
 For client-side DANE there are two new smtp transport options,
 
 
 For client-side DANE there are two new smtp transport options,


@@ -1263,9 +1300,15 @@ hosts_try_dane and hosts_require_dane.  They do the obvious thing.
 DANE will only be usable if the target host has DNSSEC-secured
 MX, A and TLSA records.
 
 DANE will only be usable if the target host has DNSSEC-secured
 MX, A and TLSA records.
 

+A TLSA lookup will be done if either of the above options match
+and the host-lookup succeded using dnssec.
+If the TLSA lookup succeeds, a TLS connection will be required
+for the host.
+

 (TODO: specify when fallback happens vs. when the host is not used)
 
 If dane is in use the following transport options are ignored:
 (TODO: specify when fallback happens vs. when the host is not used)
 
 If dane is in use the following transport options are ignored:

+  hosts_require_tls

   tls_verify_hosts
   tls_try_verify_hosts
   tls_verify_certificates
   tls_verify_hosts
   tls_try_verify_hosts
   tls_verify_certificates


@@ -1280,7 +1323,7 @@ in the delivery log line will show as "CV=dane".
 
 There is a new variable $tls_out_dane which will have "yes" if
 verification succeeded using DANE and "no" otherwise (only useful
 
 There is a new variable $tls_out_dane which will have "yes" if
 verification succeeded using DANE and "no" otherwise (only useful

-in combination with EXPERIMENTAL_TPDA), and a new variable
+in combination with EXPERIMENTAL_EVENT), and a new variable

 $tls_out_tlsa_usage (detailed above).
 
 
 $tls_out_tlsa_usage (detailed above).