The block-chain-based nLockTime solution is more elegant, but you can also use various websites (like ours at
timecave.com, which is free for simple use and recently started accepting bitcoins for an enhanced service level) that delay emails into the future. Time Cave has operated reliably for about 13 years and currently lets you schedule emails through 2025.
Of course, you'll probably want to (1) encrypt your wallet and (2) use more than one service like this, just in case.