Mailbox Rule

From the Latin English common law term; not Latin-derived..

In one sentence

An offer is accepted the moment the acceptance is mailed, not when received.

Plain English

The mailbox rule is an old contract law principle that says an acceptance becomes effective as soon as it's sent (mailed, emailed, etc.), not when the other party actually receives it. This matters because if the acceptance is lost in the mail, it still counts as a valid acceptance. The rule protects the person accepting an offer from the risk that their response gets lost. However, the rule doesn't apply to rejections or revocations, which only take effect when received.

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Example

A seller emails an offer to sell a car for $10,000, valid for 48 hours. The buyer prints out the acceptance email and mails it back the same day. Even if the mail is delayed and doesn't arrive until day three, the acceptance is valid because it was mailed on day one, before the offer expired.

Used in a sentence

“Under the mailbox rule, the contract was formed when the buyer's acceptance letter was posted, even though the seller didn't receive it for a week.”

Related terms

Revocation of Offer

A withdrawal of an offer by the person who made it, ending the other party's power to accept.

Offeree

The person who receives an offer and has the power to accept or reject it.

Lapse

An offer that expires because a deadline passes or too much time has gone by.

Contract Interpretation

The process of determining what a contract's words and terms actually mean.

Material Fact

A fact that significantly affects a party's rights, obligations, or decision-making in a contract.

Formal Contract

A contract that requires specific formalities, such as a seal, notarization, or written form, to be enforceable.

Offer

A proposal to enter into a binding agreement on specific terms.

Acceptance

Agreeing to the exact terms of an offer, creating a binding contract.

This page is a plain-English reference and is not legal advice. Laws vary by jurisdiction and change over time. For specific situations consult a licensed attorney.