ReadNotify - ReadNotify enables the user to know when email is sent and the reciever reads the email.
Hiver - Manage Customer Support, Sales and Projects right from your Gmail inbox. Collaborate with Shared Labels, Shared Contacts, email notes, email reminders and email templates
Intelliverse Email Tracker - Intelliverse Email Tracker provides insights to increase the productivity of your emails.
Clean Email - Clean Email is an online service that empowers you to take control of your mailbox.
Komiko - Komiko is a sales intelligence solution to drive sales, retention and expansion.
MailClark - The Slack bot for external communications