Transport post-delivery actions
--------------------------------------------------------------
-An arbitrary per-transport string can be expanded on successful delivery,
+An arbitrary per-transport string can be expanded upon various transport events
and (for SMTP transports) a second string on deferrals caused by a host error.
+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 set
+In order to use the feature, you must compile with
EXPERIMENTAL_TPDA=yes
in your Local/Makefile
-and define the expandable strings in the runtime config file, to
-be executed at end of delivery.
+and define one or both of
+- the tpda_event_action option in the transport
+- the delivery_event_action
+to be expanded when the event fires.
-Additionally, there are 6 more variables, available at end of
-delivery:
+A new variable, $tpda_event, is set to the event type when the
+expansion is done. The current list of events is:
-tpda_delivery_ip IP of host, which has accepted delivery
-tpda_delivery_port Port of remote host which has accepted delivery
-tpda_delivery_fqdn FQDN of host, which has accepted delivery
-tpda_delivery_local_part local part of address being delivered
-tpda_delivery_domain domain part of address being delivered
-tpda_delivery_confirmation SMTP confirmation message
+ msg:complete main per message
+ msg:delivery transport per recipient
+ msg:host:defer transport per attempt
+ msg:fail:delivery main per recipient
+ msg:fail:internal main per recipient
+ tcp:connect transport per connection
+ tcp:close transport per connection
+ tls:cert transport per certificate in verification chain
+ smtp:connect transport per connection
-In case of a deferral caused by a host-error:
-tpda_defer_errno Error number
-tpda_defer_errstr Error string possibly containing more details
+The expansion is called for all event types, and should use the $tpda_event
+value to decide when to act. The variable data is a colon-separated
+list, describing an event tree.
-The $router_name and $transport_name variables are also usable.
+There is an auxilary variable, $tpda_data, for which the
+content is event_dependent:
+ msg:delivery smtp confirmation mssage
+ msg:host:defer error string
+ tls:cert verification chain depth
+ smtp:connect smtp banner
-To take action after successful deliveries, set the following option
-on any transport of interest.
+The msg:host:defer event populates one extra variable, $tpda_defer_errno.
+
+The following variables are likely to be useful depending on the event type:
+
+ router_name, transport_name
+ local_part, domain
+ host, host_address, host_port
+ tls_out_peercert
+ lookup_dnssec_authenticated, tls_out_dane
+ sending_ip_address, sending_port
+ message_exim_id
-tpda_delivery_action
An example might look like:
-tpda_delivery_action = \
-${lookup pgsql {SELECT * FROM record_Delivery( \
+tpda_event_action = ${if = {msg:delivery}{$tpda_event} \
+{${lookup pgsql {SELECT * FROM record_Delivery( \
'${quote_pgsql:$sender_address_domain}',\
'${quote_pgsql:${lc:$sender_address_local_part}}', \
- '${quote_pgsql:$tpda_delivery_domain}', \
- '${quote_pgsql:${lc:$tpda_delivery_local_part}}', \
- '${quote_pgsql:$tpda_delivery_ip}', \
- '${quote_pgsql:${lc:$tpda_delivery_fqdn}}', \
- '${quote_pgsql:$message_exim_id}')}}
-
-The string is expanded after the delivery completes and any
+ '${quote_pgsql:$domain}', \
+ '${quote_pgsql:${lc:$local_part}}', \
+ '${quote_pgsql:$host_address}', \
+ '${quote_pgsql:${lc:$host}}', \
+ '${quote_pgsql:$message_exim_id}')}} \
+} {}}
+
+The string is expanded for each of the supported events and any
side-effects will happen. The result is then discarded.
Note that for complex operations an ACL expansion can be used.
-In order to log host deferrals, add the following option to an SMTP
-transport:
+The expansion of the tpda_event_action option should normally
+return an empty string. Should it return anything else the
+following will be forced:
-tpda_host_defer_action
+ 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
-This is a private option of the SMTP transport. It is intended to
-log failures of remote hosts. It is executed only when exim has
-attempted to deliver a message to a remote host and failed due to
-an error which doesn't seem to be related to the individual
-message, sender, or recipient address.
-See section 47.2 of the exim documentation for more details on how
-this is determined.
-Example:
-tpda_host_defer_action = \
-${lookup mysql {insert into delivlog set \
- msgid = '${quote_mysql:$message_exim_id}', \
- senderlp = '${quote_mysql:${lc:$sender_address_local_part}}', \
- senderdom = '${quote_mysql:$sender_address_domain}', \
- delivlp = '${quote_mysql:${lc:$tpda_delivery_local_part}}', \
- delivdom = '${quote_mysql:$tpda_delivery_domain}', \
- delivip = '${quote_mysql:$tpda_delivery_ip}', \
- delivport = '${quote_mysql:$tpda_delivery_port}', \
- delivfqdn = '${quote_mysql:$tpda_delivery_fqdn}', \
- deliverrno = '${quote_mysql:$tpda_defer_errno}', \
- deliverrstr = '${quote_mysql:$tpda_defer_errstr}' \
- }}
Redis Lookup
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
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.
- 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
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.
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,
-this is likely to only be usable with DANE_TA. NOTE: the
-default is to request OCSP for all hosts; the certificate
-chain in DANE_EE usage will be insufficient to validate
-the OCSP proof and verification will fail. Either disable
-OCSP completely or use the (new) variable $tls_out_tlsa_usage
-like so:
-
- hosts_request_ocsp = ${if or { {= {4}{$tls_out_tlsa_usage}} \
- {= {0}{$tls_out_tlsa_usage}} } \
+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:
+
+ hosts_request_ocsp = ${if or { {= {0}{$tls_out_tlsa_usage}} \
+ {= {4}{$tls_out_tlsa_usage}} } \
{*}{}}
-The variable 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.
-[ All a bit complicated. Should we make that definition
-the default? Should we override the user's definition? ]
+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_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
+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,
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:
+ hosts_require_tls
tls_verify_hosts
tls_try_verify_hosts
tls_verify_certificates
git://git.exim.org / exim.git / blobdiff