
The mailbox rule, also known as the posting rule, is a default principle in contract law that determines when an offer is accepted. It states that an offer is considered accepted as soon as the offeree mails their response, regardless of whether the offeror has received it. This rule applies to various means of communication, including mail, fax, telegram, and email. The mailbox rule provides clarity in contract formation and has been adapted to include electronic communications. However, it is important to note that the rule does not apply in all cases, as parties can contract around it, and it may vary across different states and countries. In the United States, the mailbox rule generally does not apply to option contracts, except in California, which follows a minority rule. While the mailbox rule originated in common law, it is important to consider specific state and country regulations when applying it in legal contexts.
| Characteristics | Values |
|---|---|
| Definition | The mailbox rule, also called the posting rule, refers to the default rule in contract law for determining when an offer was accepted. |
| Application | The mailbox rule applies to common law contracts and UCC contracts. |
| Acceptance | An offer is considered accepted when the offeree places the acceptance in the mailbox, provided that it is properly addressed and has sufficient postage. |
| Rejection | A rejection is effective when the offeror receives it. |
| Communication | The mailbox rule applies to other means of communication, such as fax, telegram, or email. |
| Exceptions | The mailbox rule does not apply to option contracts or a Merchant's Firm Offer under the UCC. |
| Variation | The mailbox rule varies from state to state in the US and from country to country. |
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What You'll Learn

Mailbox rule and the UCC
The mailbox rule, also called the posting rule, is a default rule in contract law that determines when an offer is accepted. It states that an offer is considered accepted the moment the offeree mails their letter of acceptance, rather than when the offeror receives the letter. The rule also applies to other means of communication, such as express mail, faxes, telegrams, or emails, as long as the acceptance is irrevocable once sent.
The mailbox rule originated in the British case of Adams v. Lindsell (1818), where the Court determined that the buyer accepted the seller's offer to buy wool when they responded to the seller's letter, not when the seller received the reply. This rule applies in most contract law scenarios, but it does not cover all cases. Parties can modify the mailbox rule in their contracts to specify when an offer will be considered accepted. The mailbox rule also varies across different states.
The mailbox rule applies to both common law and UCC contracts. Under the UCC, the offeree can accept in any reasonable manner unless the offeror specifies an unambiguous method of acceptance. If mailing the acceptance is considered a reasonable method, then the mailbox rule is upheld. However, if the offeror expects express notice and knowledge of acceptance, the mailbox rule would not apply.
The mailbox rule raises interesting questions when the offeree mails both an acceptance and a rejection to the offeror. In such cases, if the acceptance is mailed before the rejection, a valid contract is formed, even if the offeror receives the rejection first. The exception to this rule is if the offeror relies on the rejection before receiving the acceptance, as in the example of Garcia and the New York Yankees mentioned earlier.
In summary, the mailbox rule is a fundamental concept in contract law, applicable to both common law and UCC contracts. It determines the moment of acceptance in an offer, with potential variations and exceptions depending on the specific circumstances and jurisdictions.
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Mailbox rule and common law
The mailbox rule, also called the posting rule, is a default principle in contract law that determines when an offer is accepted. According to the mailbox rule, an offer is considered accepted as soon as the offeree posts their letter of acceptance, regardless of whether the offeror receives it. This rule provides clarity and certainty in contract formation.
The mailbox rule originated in the English case of Adams v. Lindsell (1818). In this case, the Court determined that a contract was formed when the offeree mailed their acceptance, even if the offeror had not yet received it. This established the principle that acceptance is effective upon dispatch rather than upon receipt. The mailbox rule has since been adapted to include electronic communications such as email, fax, and telegram, as long as they are irrevocable once sent.
In the United States, the mailbox rule is generally applied in common law. However, there are variations among states. For example, California follows the minority rule, applying the mailbox rule to all contracts, including option contracts. In contrast, most other states do not apply the mailbox rule to option contracts, where acceptance occurs upon receipt of the offeror's acceptance rather than when the offeree mails it.
The mailbox rule has implications for commercial transactions, providing a predictable framework for contract formation. It is important to note that the mailbox rule does not apply to instantaneous forms of communication, such as telex or electronic transactions. Additionally, the rule only applies to acceptance and not to other contractual letters, such as revocation. Parties can also contract around the mailbox rule by stipulating different terms for acceptance, requiring that acceptance is effective only upon receipt.
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Mailbox rule exceptions
The mailbox rule, also known as the posting rule, is a rule of law that specifies when an offer is accepted for the purpose of a contract. It states that an offer is considered accepted as soon as the offeree mails their letter, even if the offeror has not received it. The rule also applies to other means of communication, such as email, fax, or telegram, as long as it is irrevocable once sent.
However, the mailbox rule does have some exceptions and limitations:
Exceptions
- Option Contracts: The mailbox rule does not apply to option contracts. In these cases, acceptance is only effective when it is received by the offeror.
- Merchant's Firm Offer: The mailbox rule does not apply to a Merchant's Firm Offer under the UCC, which has a law-imposed 90-day cap.
- Counteroffers: If the offeree mails an acceptance but it arrives late, it may be considered a counteroffer. The offeror can then choose to accept or reject this counteroffer.
- Rejection Received and Relied on First: If the offeree sends an acceptance followed by a rejection, and the rejection is received and relied on first by the offeror, the mailbox rule does not apply. The contract cannot be enforced based on the acceptance.
- Unreasonable Means of Acceptance: If the offeree uses an unreasonable means of acceptance that was not specified by the offeror, the mailbox rule does not apply. Acceptance is only effective once the offeror receives it.
- Contractual Specifications: The mailbox rule is a default rule, and parties can contract around it to specify when an offer will be considered accepted.
- State-by-State Variations: The mailbox rule varies from state to state, and may not apply in all jurisdictions. For example, in California, the mailbox rule applies to option contracts, while in most other states, it applies only to bilateral contracts.
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Mailbox rule and revocation
The mailbox rule, also known as the posting rule, is a default rule in contract law that determines when an offer is accepted. It states that an offer is considered accepted as soon as the offeree dispatches their acceptance, regardless of whether the offeror receives it. This rule applies to various communication mediums, such as mail, fax, telegram, or email, provided that the acceptance is irrevocable once sent.
The mailbox rule raises questions about the timing of acceptances, rejections, and revocations. While acceptances are effective upon dispatch, rejections and revocations are only effective upon receipt by the offeror. This means that if an offeree mails an acceptance and then changes their mind, mailing a rejection, a valid contract is still formed as soon as the acceptance is dispatched. However, if the offeror receives the rejection first and relies on it, the contract cannot be enforced.
For example, if an offeree mails an acceptance on January 15 and then sends a revocation on January 16, the offeror cannot revoke the offer until they receive the revocation on January 16. In this case, the offer is considered accepted on January 15, even if the offeror does not receive the acceptance letter until a later date.
It is important to note that the mailbox rule does not apply to option contracts, where acceptances are only effective when received by the offeror. Additionally, the offeror can specify the means of acceptance, and if the offeree uses an unreasonable means, the mailbox rule may not apply, and the acceptance will only be effective upon receipt.
The mailbox rule originated in the British case of Adams v. Lindsell (1818) and has been adopted in various jurisdictions, including common law and UCC contracts. However, it may vary from state to state, and parties can contract around it to change when an offer is considered accepted.
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Mailbox rule and electronic communications
The mailbox rule, also known as the posting rule, is a default principle in contract law that determines when an offer is accepted. According to the mailbox rule, an offer is considered accepted once the offeree places their acceptance in the mailbox, provided it is properly addressed and has sufficient postage. This rule provides clarity and certainty in contract formation, especially in situations where parties do not negotiate face-to-face.
The mailbox rule originated in the British case of Adams v. Lindsell (1818), where the Court determined that a contract was formed when the offeree mailed their acceptance, regardless of whether the offeror had received it. This established the principle that acceptance is effective upon dispatch rather than upon receipt. The mailbox rule generally applies to common law contracts for services, but there is some debate about its applicability to contracts for goods.
In the digital age, the mailbox rule has been extended to include electronic communications such as email. Courts may apply similar principles to determine when acceptance occurs in electronic contexts. However, the specific rules regarding electronic communications are still evolving, with some countries enacting legislation based on the UNCITRAL Model Law of Electronic Commerce. The Electronic Transactions Act, for example, suggests that the "`received' rule should apply to electronic communications", but this interpretation is not universally accepted.
It is important to note that the mailbox rule does not apply to all cases. Parties can contract around the mailbox rule and stipulate different terms for acceptance in their agreements. For instance, they can specify that acceptance is only effective upon receipt rather than dispatch. Additionally, the mailbox rule does not apply to instantaneous forms of communication, such as telephone or telex, where acceptance occurs when communicated.
In summary, the mailbox rule, including its adaptation to electronic communications, plays a crucial role in contract law by providing a predictable framework for contract formation. It ensures that acceptance is effective upon dispatch, bringing certainty to the contract formation process. However, it is essential to be aware of the variations in the application of the mailbox rule across different states, countries, and types of contracts.
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Frequently asked questions
The mailbox rule, also called the posting rule, is a default principle in contract law that determines when an offer is accepted. According to the mailbox rule, an offer is considered accepted when the offeree places the acceptance in the mailbox, regardless of whether the offeror receives it.
Yes, the mailbox rule is an exception to the general rule of contract law in common law countries. It originated from the English case of Adams v. Lindsell (1818).
The mailbox rule applies to mail, fax, telegram, and email. In some cases, it has also been applied to electronic communications, such as in California, where the mailbox rule is applied to all contracts.
Yes, the mailbox rule is a default rule and does not apply in all cases. Parties can contract around it by stipulating different terms for acceptance in their agreements, such as requiring acceptance only upon receipt rather than dispatch.






















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