https://uglyemail.com/
Ugly Email - Gmail extension for blocking read receipts and other email tracking pixels.
The #1 most downloaded Gmail extension for blocking read receipts and other email tracking pixels.
ugly emailgmail extension
https://www.readnotify.com/default.asp/from/1netcen
Certified email with delivery receipts, silent tracking, proof-of-opening history, security and...
Users get free return email notifications, and/or SMS/ICQ instant messages when email they've sent gets opened, and can track their emails reading history