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
GoDaddy Email & Office - Other Email
Clean Email - Clean Email is an online service that empowers you to take control of your mailbox.
Boomerang for Outlook - Boomerang for Outlook offers email productivity tools to track, schedule and send mails at the right time.
MailClark - The Slack bot for external communications
BlueMail - BlueMail is an email management app for Android, iOS, and Windows.