The postal acceptance rule, also called the mailbox rule, is a contract law regarding the mailing of acceptance or offer letters through the postal system.
The postal acceptance rule states that a contract is made when a person mails a letter from the person's mailbox or a general mailing centre. The rule states that when the letter is mailed, the person assumes that acceptance is deemed to occur, meaning the letter will reach its destination.
This rule is used in the case of accepting offers. For example, if a purchaser of a property accepts an offer made by a seller by sending an acceptance letter to the seller, the seller cannot retract the offer once the letter is mailed, regardless of receiving the letter or not.
Once an offer of acceptance or an agreement is made and one party mails a letter stating this, the offer is considered valid. This offers an advantage to prospective buyers, allowing the offer to remain valid once the letter is mailed. Once the acceptance letter is mailed, the deal becomes a legally binding contract.