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 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 tpda_event_action option in the transport
+- the delivery_event_action
+to be expanded when the event fires.
A new variable, $tpda_event, is set to the event type when the
expansion is done. The current list of events is:
- msg:delivery
- msg:host:defer
- tcp:connect
- tcp:close
- tls:cert
- smtp:connect
+ 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
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
The msg:host:defer event populates one extra variable, $tpda_defer_errno.
-The following variables are likely to be useful for most event types:
+The following variables are likely to be useful depending on the event type:
router_name, transport_name
local_part, domain
tls_out_peercert
lookup_dnssec_authenticated, tls_out_dane
sending_ip_address, sending_port
+ message_exim_id
An example might look like:
'${quote_pgsql:$message_exim_id}')}} \
} {}}
-The string is expanded after the delivery completes and any
+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.
-During the expansion the tpda_event variable will contain the
-string-list "msg:delivery".
-
The expansion of the tpda_event_action option should normally
return an empty string. Should it return anything else the
msg:delivery (ignored)
msg:host:defer (ignored)
+ msg:fail:delivery (ignored)
tcp:connect do not connect
tcp:close (ignored)
tls:cert refuse verification
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
+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:
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
it has the default value of "*". Admins who change it, and
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