SendRecurring - SendRecurring allows you to setup, send, and maintain scheduled email reminders.
NeverBounce - Real-time email verification and cleaning to ensure emails never bounce.
Recurrr - Send recurring emails
Email List Verify - The Fastest Way to Improve Email List Deliverability and ROI
FollowUpThen - The simplest way to schedule an email reminder
DeBounce - Email Validation, Email Checker, Data Enrichment and Appending Tool. Using DeBounce remove invalid, disposable, spam-trap, syntax and deactivated emails.