Log envelope id MTA option

Transaction logging MTA options:  (0-7)
(New in MS 6.1.) The  MTA option controls whether or not the envelope ID (ENVID parameter of the MAIL FROM ESMTP command) is included in   records and    mapping probes. This information may be useful when tracking a message across multiple systems. The default is 0, meaning that the field is not logged. Setting bit 0 (value 1) causes the envelope ID to be logged, immediately after the message filename field and immediately before the  message-id field. In XML or JSON format ( set to 4 or 5, respectively), envelope ID logging, if enabled, appears as the   attribute. New in 7.0-3.01, bit 1 (value 2), if set, causes the information to be included in   mapping probes.

Normally the  attribute only appears in XML or JSON format logs if there is envelope id information to log. As of MS 8.0.2.3, setting bit 2 (value 4) will cause the attribute to appear unconditionally.

See also:
 * Transaction logging MTA options
 * MTA transaction logging
 * Triggering effects from transaction logging with LOG_ACTION
 * log_format MTA Option