In their FAQ nothing is sent to the recepient until the letter is sent. This seems like such a great service until you realize email providers, and addresses aren't permanent.

I've been with my husband 20+ years, I had 10+ email addresses when we met, and so did he. I love the idea, but wish there was a non-digital option for these things.

Digitally, if we could register a non-first-level domain for 40-50 years we could set up our own family email severs, with scheduled messages.