Read tracking lets you know if the email you’ve sent has been read or not and Canary lets you do just that.
Read Tracking on your macOS device
By default Read receipt is enable.
Note: Once your email has been read, a notification will be sent to you and Canary blocks all tracking services.
Using the Activity Stream
Click on your Read Activity icon to track which of your emails have been read.
The Read Activity window displays all your emails that have been read by the recipient.