reserve_maintenance_interval — how often to perform mail queue maintenance
reserve_maintenance_interval = 15
This option specifies how often to perform mail queue maintenance to evaluate whether reserved connections should be established to get mail out of the system.
The system will usually limit the number of connections to
server_max_outbound_connections, but during the reserve sweep, will allow up to
reserve_outbound connections to be established.
The system will respect any limits that have been defined, the reserve mechanism will not cause more connections to be established beyond a defined limit for a particular domain.
The default value for this option is
reserve_maintenance_interval is valid in the global scope.