FollowUpThen - The simplest way to schedule an email reminder
Future Me - Send an email to your future self
SendRecurring - SendRecurring allows you to setup, send, and maintain scheduled email reminders.
Letter to Yourself - Send a physical letter to your future self
Laytr - Laytr is the easiest way to defer emails.
Letter to my future self - Letter to my future self is a prominent email scheduling service that gives you the opportunity to create a letter with goals and thoughts for your future self and schedule a date for sending it.