Hello there! Alternatively, you can use FutureMe, its on the Suicide Compilation Thread, based on personal experience. It can be to yourself too in the event you feel like it is not your time yet.
You will not be able to read the letter after a couple days, whereas you'd still be able to on Gmail, to prevent any triggers/second thoughts after reading if any. Apologies if my english is bad.
Program an email to be sent in the future:
https://www.futureme.org/
All the best and see you on the other side~