Yale law professor Ian Ayres examines Adams v. Lindsell, the classic English case that established the mailbox rule in contract formation. This lecture is drawn from his American Contract Law course and looks at how courts decided that acceptance of an offer becomes effective the moment a letter is posted, not when it is received, even when the letter goes astray. Ayres walks through the facts of the misdirected missive at the center of the case and the timing problems it created for offer and acceptance, then uses it to explain why the rule allocates risk the way it does between offeror and offeree. The lecture fits within a broader unit on silence as acceptance and the mechanics of the bargain relationship, treating this eighteen-minute case study as a building block for understanding when and how a contract actually comes into existence.