EasyEmail - Gmail plug-in that helps you write emails quickly
Clean Email - Clean Email is an online service that empowers you to take control of your mailbox.
Text Case - Format any raw text on iOS and more 📝
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
Really Good Emails - A large collection of good product email design.
MailClark - The Slack bot for external communications