Sendmail, 3rd Edition

Name

SingleThreadDelivery

Synopsis

Ordinarily, when sendmail processes the queue, it pays relatively little attention to other sendmail processes that might be processing the same queue at the same time. It locks a single qf file during delivery so that no other sendmail will attempt delivery of that message at the same time, but that is all. When sending many messages to a single other host, it is possible for multiple, parallel sendmail processes to try to deliver different messages from that queue to that single host all at once.

When parallelism is not desirable, you might wish to set up sendmail to be single-threaded. This ensures that only a single sendmail will ever be delivering to a given host at a given time. Single-threaded delivery is enabled with the SingleThreadDelivery option, the forms of which are as follows:

O SingleThreadDelivery=bool                ← configuration file (V8.8 and later) 
-OSingleThreadDelivery=bool                ← command line (V8.8 and later) 
define(`confSINGLE_THREAD_DELIVERY',`bool')← mc configuration (V8.8 and later) 

The argument bool is of type Boolean. If it is missing, the default value is true (deliver single-threaded). If the entire SingleThreadDelivery option is missing, the default becomes false (deliver in parallel). The default for the mc configuration technique is false.

Note that the SingleThreadDelivery option will work only if the HostStatusDirectory option is also declared (HostStatusDirectory). If it is not, sendmail will print the following error and reset ...