Service group

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Besides a few options affecting Dispatcher operation as a whole, or set directly at the dispatcher level to establish defaults for Dispatcher services lacking their own specific settings, the primary way that Dispatcher options are set is within named service groups, to define specific Dispatcher services. Each such named service has associated ports (established via the tcp_ports and/or ssl_ports options); the Dispatcher listens for TCP connections on those ports, and then hands off the connections to Worker Processes for the named service, where the Worker Process will then execute the image specified for that service.

For instance, at its most basic, in principle the SMTP service could be defined as:

msconfig> set dispatcher.service:SMTP.tcp_ports 25
msconfig# set dispatcher.service:SMTP.image IMTA_BIN:tcp_smtp_server
msconfig# set dispatcher.service:SMTP.enable 1

More typically, however, additional options, such as a logfilename and perhaps parameter as well as various options tuning performance would be set also; while since the enable Dispatcher service option defaults to 1, and as of MS 7.0.5 the named SMTP service defaults to the image shown, in reality neither of those options needs to be explicitly set.

Within a named Dispatcher service group, besides the port tcp_ports and/or ssl_ports) and image option settings establishing the correspondence between port(s) and service, many other Dispatcher option settings are available to specify and further control operation of that service: thresholds at which to create new or additional server processes, age at which to expire "old" server processes, etc.

Thus in particular note that in MTA terminology and operation, a Dispatcher service such as the SMTP service encompasses potentially multiple (transient) SMTP server processes: the SMTP server processes come and go, created and expired as needed by the Dispatcher, within the parameters established in the Dispatcher's SMTP service definition.

Note that special symbolic names known to the MTA -- such as IMTA_BIN and IMTA_LOG -- are supported (and convenient) for values of service group options.

See also: