Drip Drop Email VS DidTheyReadIt

ContactMonkey - ContactMonkey tracks email opens and link clicks.

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.

GetNotify - GetNotify is a free email tracking software solution.

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

WhoReadMe - WhoReadMe is an email tracking solution that provides details on read duration, recipient location, organization name, operating system etc.