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

ReadNotify - ReadNotify enables the user to know when email is sent and the reciever reads the email.

Recurrr - Send recurring emails

GetNotify - GetNotify is a free email tracking software solution.

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.

WhoReadMe - WhoReadMe is an email tracking solution that provides details on read duration, recipient location, organization name, operating system etc.