title: What is the best Java-based Mailing List application allowing opt-in/opt-out
body: <p>I'm looking for a java-based (preferable) mailing list application that allows users to opt-in/opt-out of mailing lists.  Open-source is preferable but not mandatory.</p>
  
  <p>This product would be used to send email notifications to subscribed people when certain events happen in another application - i.e.  when a new record is saved and approved with certain attributes, a message is sent to one or more mailing lists.  </p>
  
  <p>It should be able to handle multiple mailing lists and must have an interface for sending new messages programatically without the need to use it's web/gui interface.</p>
  
  <p>A last resort would be to develop our own application to perform this functionality.</p>