Free Gmail tracking with geolocation. With GeoTrack, track if your emails were read, clicked, recipient's geolocation, device used and much more...
Mailtrack.io - The best email tracking solution I've found. Free
iTrackmail - Want to know if people are reading the emails you send?
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.
Terminus App - Terminus is a feature-rich URL builder that helps you build and manage your UTM tracking URLs.
GetNotify - GetNotify is a free email tracking software solution.