We are having problems with duplicate mailings being sent out. John Doe may be listed more then once in CiviCRM - For example, John Doe and Doe, John but it's the same addressee. What can I do to rectify the matter so that only one mailing will go out to this addressee versus two?
I believe you should eliminate the duplication in your database. The CRM provides a tool for handling the duplicated contacts. You can merge the duplicated contacts into a single one. With this the email addresses will be unique so that only one email will be sent.