I'm looking for a word that could be used for a letter that should only be opened after a specified date or time.

For example a letter written for an 18th birthday, the letter could be written years before but shouldn't be opened until the individuals 18th birthday.

There's an example in the TV series 'Dark'. Michael Kahnwald writes "Do not open before November 4, 10:13 P.M." on the envelope of a suicide note.


I don't think 'testament' is correct, taken form 'Last will and testament' a legal document read on a persons death.

It might just be that there is no name for this as all letters are opened in the future?

  • 3
    The word does not exist.
    – Greybeard
    Commented Nov 21, 2021 at 13:34
  • 1
    What you're describing is a bit similar to the concept of a "dead man's switch", i.e. something that the originator wants to happen at a certain time or upon certain conditions even when he or she is not present. The Wikipedia article says that the UK prime minister writes "letters of last resort" to be opened in case the government is incapacitated. Commented Nov 21, 2021 at 15:34
  • A time capsule is similar to this idea, but a time capsule is more long-term.
    – turkey
    Commented Nov 21, 2021 at 20:39

2 Answers 2


I've seen the term Open When letter used for this sort of thing, although it's not a particularly common phrase. It can be a specific date like a birthday, a general "open when you graduate" , or "open when you're sad or lonely". The derivation of the name is obvious.

Here are a couple of crafting blogs that mention the idea:


Is your name Marty McFly?

Some customers are using Future Mail to send letters to their future selves, others use it to be sure their anniversary, birthday, or holiday greetings will arrive exactly on time. Future Mail customers simply fill out, address their cards, letters, or packages, and specify the date they want them delivered. These new companies will make it happen. One can even purchase gifts and flowers to be sent in the future.

When signing up for the service, customers are assessed a fee depending on how long the company has to hold on to the deliverables. Customers must also provide current contact information, in case their item is undeliverable in the future. Once the letter or package is handed over, the company tucks it away in a safe place until the date selected comes around. Though some customers have concerns about what happens to their packages if the companies fail, the service continues to catch on. — USPS: Mail to the Future?

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