Delivery Mode

Delivery Mode

One configuration option frequently overridden on the command line is the d option, which specifies the sendmail delivery mode. The delivery mode determines how quickly mail is delivered:

i: deliver interactively (synchronously)
b: deliver in background (asynchronously)
q: queue only (don't deliver)

There are trade-offs. Mode i passes the maximum amount of information to the sender, but is rarely necessary.

Mode q puts the minimum load on your system, but if you use it, delivery may be delayed for up to the queue interval.

Mode b is probably a good compromise. However, in this mode, sendmail may initiate a large number of processes if you have a mailer that takes a long time to deliver a message.