In the United States (U.S.), the mail box rule, also known as the postal rule or presumption of receipt rule, is a legal doctrine that states the acceptance of a contract is effective upon its posting to the U.S. mail. This rule is an exception to most contract law in countries that follow common law, which states contracts are effective upon communication. Contracts can include such items as tax payments, insurance premiums and utility payments. Under this legal principle, once the sender has mailed a letter, he can presume the sender has received it; the recipient regards the contract as on-time based on the postmark date.
When it comes to forms of payment, a payment is said to have been made on the date the payer properly mailed his check in a mailbox or handed it to a postal employee. As such, many companies that receive payment will refer to the postmark date, not the date it actually received the payment, when determining whether a payment was made on time.
There have historically been challenges to this law. Some argue that common sense should prevail when mailing a contract or a payment. If a sender knows, for example, there was a fire in their apartment building's mail room the day they left their letter to be sent out, he or she really can't presume the letter was sent to its recipient.
Delivery service also can be an issue. U.S. Courts have issued conflicting rulings as to whether a postmark or confirmation of receipt from a delivery service other than the U.S. Postal Service meets the criteria of the mail box rule. In the United States, at least, it is probably wise to only use the U.S. Postal Service if the sender suspects the mail box rule might need to be invoked.
Getting proof of mailing may also be a good idea. While a postmark from the official postal service usually is sufficient for proving date of mailing, there are times when a letter might get lost in the post office and not actually be postmarked for a few days. Also, a postmark from an office postage meter may not itself be sufficient under the mail box rule. Senders may best protect themselves by bringing their letter to the post office and asking for proof of mailing; for even greater protection, consumer can request a tracking service and proof of receipt.