In some cases you may find that the queue has gotten clogged for some reason. You can force a queue run using the -q flag (with no value). It is entertaining to use the -v flag (verbose) when this is done to watch what happens:
You can also limit the jobs to those with a particular queue identifier, sender, or recipient using one of the queue modifiers. For example, -qRberkeley restricts the queue run to jobs that have the string berkeley somewhere in one of the recipient addresses. Similarly, -qSstring limits the run to particular senders and -qIstring limits it to particular queue identifiers.