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

Komiko - Komiko is a sales intelligence solution to drive sales, retention and expansion.

Recurrr - Send recurring emails

Mailtrack.io - The best email tracking solution I've found. Free

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.

Bananatag - Find out what happens to your emails after you press send! Add email tracking, attachment tracking, email scheduling and templates to your daily emails.