Mailing an envelope to your self does not allow other people to verify whether the envelope wasn’t opened in between.
Maybe a quality forensic lab has the ability to tell whether the envelope was opened in between but most people you might show the letter don’t.
Also, it’s a lot easier to fake by writing 10 letters with 10 different predictions and then burning the ones that don’t come true.
Mailing an envelope to your self does not allow other people to verify whether the envelope wasn’t opened in between.
Maybe a quality forensic lab has the ability to tell whether the envelope was opened in between but most people you might show the letter don’t.
Also, it’s a lot easier to fake by writing 10 letters with 10 different predictions and then burning the ones that don’t come true.