LFS = Looking For Service

TL;DR: can you recommend me a service to send myself emails at a later date that works like a time capsule so that the email can not be deleted or seen by someone else (except the service provider obviously)?

LT;MR(= Long Text; Might Read): Lately I've been trying to pay attention to the passage of time by celebrating the solar-events (summer/winter solstice and autumn/spring equinox).

For this years autumn equinox celebration I would like myself and my guests to send ourselves an email that arrives a week before next years spring equinox to our own email addresses.

The prompt will be: What would you like to do more of this coming summer?

I understand many common email clients/providers support this natively but it's my understanding those emails end up in specific folder so they are easy to find and subsequently read and/or delete which negates the idea I want to accomplish.

So, I'm looking for a service to store and send those emails to me and my guests in time for next years spring equinox.

Thank you 🥰