Doubletick is an email tracking tool. It tells you if your emails have been opened by the recipient or not, It shows double ticks ✓✓ (checkmarks) in your Gmail sent box if mail is read by the recipient. It also notifies you with a desktop notification when the is opened.
Downloading and Installing Doubletick is very easy, In Chrome Browser, Click on Link to download and install Chrome Extension
After download and installation of Doubletick Chrome Extention, once you connect your account with Google Account / Gmail, Your sent emails will be automatically tracked. If not working, you can close and reopen your chrome browser after insallation and login.