R2d § 63
Time When Acceptance Takes Effect
Unless the offer provides otherwise, (a) an acceptance made in a manner and by a medium invited by an offer is operative and completes the manifestation of mutual assent as soon as put out of the offeree's possession, without regard to whether it ever reaches the offeror; but (b) an acceptance under an option contract is not operative until received by the offeror.
Professor's notes
Elements: (a) acceptance made in a manner invited by the offer is operative as soon as put out of the offeree's possession, regardless of whether it ever reaches the offeror; (b) acceptance under an option contract is operative only on receipt.
This is the mailbox rule. Dispatch governs acceptances; receipt governs revocations, rejections, and counteroffers (§ 40, § 42).
Common misunderstanding: students think the mailbox rule sets one timing rule for everything. It does not. Two regimes are running in parallel: dispatch for acceptances, receipt for everything else: and the asymmetry favors the offeree. Note also the option-contract carve-out in 63(b): once consideration locks the offer open, fairness flips to receipt.
Doctrinal status: pure chok: a formal rule of timing, picked for administrability rather than for any independent moral content.
Text
R2d § 63. Time When Acceptance Takes Effect.
Unless the offer provides otherwise,
(a) an acceptance made in a manner and by a medium invited by an offer is operative and completes the manifestation of mutual assent as soon as put out of the offeree’s possession, without regard to whether it ever reaches the offeror; but
(b) an acceptance under an option contract is not operative until received by the offeror.