The postbox rule makes it clear that, when people choose to communicate by mail, they take the risk of delay or loss, and the acceptance as a result will be binding only when or if received.

The postbox rule, also known as the mailbox rule, states that an acceptance becomes effective, and thus a contract is formed, at the time the acceptance is sent by the offeree, not when it is received by the offeror. This means that the risk of delay or loss in the mail falls on the offeror, not the offeree.