The following option applies only when Sendmail is used in Unix/Linux environments.

When sending a large number of emails with the mailer engine, processing delays may be caused by attempts on the part of the mail server to locate the destination domain of each email. As a consequence, timeouts may occur causing failure of the cron ask. Or the cron task may be triggered before the previous instance has terminated. In the latter case, some emails may be sent multiple times.

Such problems may be avoided by using the Sendmail deferred delivery mode. In this mode, each email is simply put on a queue for later processing by Sendmail. This results in much faster response to the cron task.

You may enable the deferred delivery mode by setting the corresponding variable on the installation screen of this extension. The option applies only to emails sent by the mailer engine cron task of the Direct Mail extension.

The following variables must be set in the Sendmail configuration file (values shown here are just examples):

DAEMON=yes

SMQUEUE=10m

QUEUE=30m

These example settings have the following meaning: the email queue will be emptied every 10 minutes. If a problem is encountered while trying to send an email, it will be put on another queue and delivery will be attempted again every 30 minutes.

For more information on Sendmail configuration, see: http://www.sendmail.org/.