MAILBOX RULE

mailbox rule. 1. Contracts. The principle that an acceptance becomes effective — and binds the offeror — once it has been properly mailed. • The mailbox rule does not apply, however, if the offer provides that an acceptance is not effective until received. [Cases: Contracts 22(1).C.J.S. Contracts §§ 46–51, 53–54; Trading Stamps and Coupons§§ 7–9.] […]