The Chrome extension adds a "Send with Dmail" button next to the regular "Send" button in any email you compose.

This gives you complete control to revoke sent emails. You can preset timing such as "in 1 hour" or "in 1 week" and the message will self-destruct accordingly.

If you don't have a predetermined time frame, you can tell the system to never delete but if you change your mind you can find the email in your sent folder and do so.

All messages are encrypted and whenever the sender restricts the right to access, the recipient will no longer be able to see the original message.

Dmail claims that they will soon unlock a feature where only the intended recipient can see your message.
Sadly you can only send such messages through Gmail on Chrome.