Clogged mail queues
In some cases, you might find that the queue is clogged for some reason. You can force a queue to run using the -q flag (with no value).
You can also use the -v flag (verbose) to watch what happens:
/usr/sbin/sendmail -q -v
You can also limit the jobs to those with a particular queue identifier,
sender, or recipient using one of the queue modifiers. For example, -qRsally restricts
the queue run to jobs that have the string
sally in one of
the recipient addresses. Similarly, -qSstring limits
the run to particular senders, and -qIstring limits
it to particular queue identifiers.