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Chapter 60 - Events

The events mechanism in Exim can be used to intercept processing at a number of points. It was originally invented to give 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:

event_action = ${if eq {msg:delivery}{$event_name} \
{${lookup pgsql {SELECT * FROM record_Delivery( \
    '${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}')}} \
} {}}

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:

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

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:

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

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 contexts that Exim operates in during the course of its processing:

  • variables set in transport events will not be visible outside that transport call

  • acl_m variables in a server context are lost on a new connection, and after smtp helo/ehlo/mail/starttls/rset commands

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:

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

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.

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