[Bounty 420 ETH] Implement a method for verifying a message has been received when sent over unreliable channels

[NovemberOrWhatever]

In order to properly buy and sell geese over the blockchain, it is necessary that one user can send a message, another user can receive the message, and the first user can be 100% sure the message was received, while the second user is 100% sure the first user knows their message was received, despite communication platforms not being 100% reliable. This should be a good first issue