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

SendRecurring - SendRecurring allows you to setup, send, and maintain scheduled email reminders.

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

Recurrr - Send recurring emails

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

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.