ReadNotify - ReadNotify enables the user to know when email is sent and the reciever reads the email.

EmailTrackerPro - EmailTrackerPro is an email tracking and spam filter solution.

Intelliverse Email Tracker - Intelliverse Email Tracker provides insights to increase the ​productivity of your emails.

DidTheyReadIt - DidTheyReadIt e-mails that are sent will be invisibly tracked and the instant the recipient opens the message DidTheyReadIt automatically notifies the user.

Mixmax - At Mixmax, our mission is to change how the world communicates. We’re an email productivity platform that helps sales, customer success, and recruiting teams do their jobs better.

GetNotify - GetNotify is a free email tracking software solution.