SendRecurring - SendRecurring allows you to setup, send, and maintain scheduled email reminders.
Brevo - Innovative online Email Marketing solution to manage your contacts, create & send your newsletters and track your results. More than 80 000 clients. Best prices and attractive features.
Recurrr - Send recurring emails
RGB Technologies - Email Scheduler - Email Scheduler provides an intuitive email scheduling solution, integrated within the existing Salesforce account.
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.
SndLatr - SndLatr is a Gmail plugin that makes it easy to schedule emails to be sent automatically at a later time.