What is the open rate of your emails? And who exactly opened them? This metric is clearly essential to understand the efficiency of an email campaign. A low open rate may mean that your subject line is not catchy enough, or that many subscribers have lost interest in your communications: in any case, you'll need to revise your strategy.
To get this information we recommend to enable turboSMTP's open tracking tool. All the openings will be recorded and showed both in the statistics chart and in the email feed, highlighting which users have actually opened (and hopefully read!) your message.