Right Inbox - Schedule Emails in Gmail To Be Sent Later
Future Me - Send an email to your future self
Recurrr - Send recurring 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.
FollowUpThen - The simplest way to schedule an email reminder
Letter to Yourself - Send a physical letter to your future self