EmailTrackerPro - EmailTrackerPro is an email tracking and spam filter solution.
ReadNotify - ReadNotify enables the user to know when email is sent and the reciever reads the email.
Bananatag - Find out what happens to your emails after you press send! Add email tracking, attachment tracking, email scheduling and templates to your daily emails.
Sendia - Send cold email in seconds with Sendia, an outreach tool for Gmail that's free & easy to use!
Intelliverse Email Tracker - Intelliverse Email Tracker provides insights to increase the productivity of your emails.
ifRread - ifRead is a free email tracking service that tracks email you sent.