Contracts I

Restatement Second of Contracts § 63

Time When Acceptance Takes Effect

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Unless the offer provides otherwise,

1. 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
2. an acceptance under an option contract is not operative until received by the offeror.

Restatement Second of Contracts § 66

Acceptance Must Be Properly Dispatched

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An acceptance sent by mail or otherwise from a distance is not operative when dispatched, unless it is properly addressed and such other precautions taken as are ordinarily observed to insure safe transmission of similar messages.

Restatement Second of Contracts § 40

Time When Rejection or Counter-Offer Terminates the Power of Acceptance

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Rejection or counter-offer by mail or telegram does not terminate the power of acceptance until received by the offeror, but limits the power so that a letter or telegram of acceptance started after the sending of an otherwise effective rejection or counter-offer is only a counter-offer unless the acceptance is received by the offeror before he receives the rejection or counter-offer.