SoftTweak OST Converter VS The Very good 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

Nylas Mail - The Nylas Cloud API powers your application with email, calendar & contacts features. Built-in features for better email, calendar, and contact management.

Clean Email - Clean Email is an online service that empowers you to take control of your mailbox.

MailClark - The Slack bot for external communications

Email Signature Rescue - Create, manage and deploy beautiful customized HTML signatures in any email client.

DuoCircle - DuoCircle provides enterprise spam filtering and email management solutions.