This MaxRunnersPerQueue option defines the maximum number of queue processors that can run in parallel in any given queue group. Note that this differs from the MaxQueueChildren option (MaxQueueChildren), which sets the total limit for all queue processors.

The MaxRunnersPerQueue option is declared like this:

O MaxRunnersPerQueue=num                    configuration file (V8.12 and later) 
-OMaxRunnersPerQueue=num                    command line (V8.12 and later) 
define(`confMAX_RUNNERS_PER_QUEUE', `num')  mc configuration (V8.12 and later) 

Here, num is of type numeric. If num is negative, nonnumeric, or zero, no limit is set. If num is positive (the default is 1), that limit is applied to each queue group.

Note that this limit is overridden by the Runners= equate, of the Q configuration file lines (Section 11.4.2), and that a Runners=0 disables all queue processing for a queue group. If a Runners= is not specified for a queue group, this MaxRunnersPerQueue option sets the default. Also note that this MaxRunnersPerQueue option is effective only if the MaxQueueChildren option is also given a positive value.

The MaxRunnersPerQueue option is not safe. If specified from the command line, it can cause sendmail to relinquish its special privileges.