Which of the below rules allows that an acceptance is valid when it is placed in the mailbox?

A) The Acceptance Rule
B) The Contract Rule
C) The Reasonable Rule
D) The Mailbox Rule
E) The Contract Legality Rule

The Mailbox Rule, also known as the postal rule, is a legal principle that states an acceptance is considered effective once it is dispatched by the offeror, not when it is received by the offeror. This rule applies primarily to contract law, making the communication of acceptance complete as soon as the letter of acceptance is placed in the control of the postal service.