With Mailster you get many details from your subscribers: clicks, opens, unsubscriptions and bounces. If you watch your websites visitors via an analytics system like Google Analytics or Piwik you can now track you newsletter campaigns with them too.
I’ve released two free add-on on the WordPress repository which are easy to setup.
Google Analytics Extension
after activation you can access a new tab on the settings page:
You can define the parameters for each campaign separately