Send your future self an email through FutureMe

https://www.futureme.org/

You can use the site to

• create an account (free),
• type up an email to yourself (free),
• set the time you want the email delivered (one year from now? five years from now? on your fortieth birthday? on the Fourth of July ten years from now? the possibilities are endless...) (free),
• make sure your email address is right (or you won't get the email!) (free),
• decide whether you want the email kept private or be made public (you can ask that it be public but anonymous) (I'm not sure if you have to have a paid account for the private option),
• and send (free).

Or you can skip the part about creating an account and writing yourself an email; just read some of the emails-to-myself that others have made public (free). Are they real? I have no idea.

I'm not clear on what the paid account entails.

They also have clever ideas for teachers to use a paid account as a way for students to write letters to themselves (accessible only by the teacher).