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.

Gmelius - Gmelius is the first collaboration platform designed for G Suite and your company's daily tools.

GetNotify - GetNotify is a free email tracking software solution.

Mailtrack.io - The best email tracking solution I've found. Free

Followup.cc - FollowUp for email is a lightweight productivity suite that keeps your conversations and tasks from slipping through the cracks. Set perfectly timed reminders that arrive at the top of your inbox, right when you need them.

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