+.chapter "Events" "CHAPevents" &&&
+ "Events"
+.cindex events
+
+.new
+The events mechanism in Exim can be used to intercept processing at a number
+of points. It was originally invented to giave a way to do customised logging
+actions (for example, to a database) but can also be used to modify some
+processing actions.
+
+Most installations will never need to use Events.
+The support can be left out of a build by defining DISABLE_EVENT=yes
+in &_Local/Makefile_&.
+
+There are two major classes of events: main and transport.
+The main configuration option &%event_action%& controls reception events;
+a transport option &%event_action%& controls delivery events.
+
+Both options are a string which is expanded when the event fires.
+An example might look like:
+.cindex logging custom
+.code
+event_action = ${if eq {msg:delivery}{$event_name} \
+{${lookup pgsql {SELECT * FROM record_Delivery( \
+ '${quote_pgsql:$sender_address_domain}',\
+ '${quote_pgsql:${lc:$sender_address_local_part}}', \
+ '${quote_pgsql:$domain}', \
+ '${quote_pgsql:${lc:$local_part}}', \
+ '${quote_pgsql:$host_address}', \
+ '${quote_pgsql:${lc:$host}}', \
+ '${quote_pgsql:$message_exim_id}')}} \
+} {}}
+.endd
+
+Events have names which correspond to the point in process at which they fire.
+The name is placed in the variable &$event_name$& and the event action
+expansion must check this, as it will be called for every possible event type.
+
+The current list of events is:
+.display
+&`msg:complete after main `& per message
+&`msg:delivery after transport `& per recipient
+&`msg:rcpt:host:defer after transport `& per recipient per host
+&`msg:rcpt:defer 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
+.endd
+New event types may be added in future.
+
+The event name is a colon-separated list, defining the type of
+event in a tree of possibilities. It may be used as a list
+or just matched on as a whole. There will be no spaces in the name.
+
+The second column in the table above describes whether the event fires
+before or after the action is associates with. Those which fire before
+can be used to affect that action (more on this below).
+
+An additional variable, &$event_data$&, is filled with information varying
+with the event type:
+.display
+&`msg:delivery `& smtp confirmation mssage
+&`msg:rcpt:host:defer `& error string
+&`msg:rcpt:defer `& error string
+&`msg:host:defer `& error string
+&`tls:cert `& verification chain depth
+&`smtp:connect `& smtp banner
+.endd
+
+The :defer events populate one extra variable: &$event_defer_errno$&.
+
+For complex operations an ACL expansion can be used in &%event_action%&
+however due to the multiple contextx that Exim operates in during
+the course of its processing:
+.ilist
+variables set in transport events will not be visible outside that
+transport call
+.next
+acl_m variables in a server context are lost on a new connection,
+and after smtp helo/ehlo/mail/starttls/rset commands
+.endlist
+Using an ACL expansion with the logwrite modifier can be
+a useful way of writing to the main log.
+
+The expansion of the event_action option should normally
+return an empty string. Should it return anything else the
+following will be forced:
+.display
+&`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
+.endd
+No other use is made of the result string.
+
+For a tcp:connect event, if the connection is being made to a proxy
+then the address and port variables will be that of the proxy and not
+the target system.
+
+For tls:cert events, if GnuTLS is in use this will trigger only per
+chain element received on the connection.
+For OpenSSL it will trigger for every chain element including those
+loaded locally.
+.wen
+
+. ////////////////////////////////////////////////////////////////////////////
+. ////////////////////////////////////////////////////////////////////////////
+
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