In some cases, you may want an automatic email, or a newsletter to only go to a certain subset of customers. Perhaps your "Event Reminder" email contains a lot of information about delivery details, and you don't want that email going to customers with the Deliver Type "Fully Staffed".
InflatableOffice uses the filters from the leads page to accomplish this. First, filter your leads on the leads page and save the filter.
Then go to Settings -> Email Center, and edit the template you want to apply the filter to. Go to restrictions and add the filter there and save.