
The mailbox rule, also known as the posting rule, is a fundamental principle 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 was established in the British case of Adams v. Lindsell (1818), where the Court decided that a contract was formed when the offeree mailed their acceptance, even if the offeror had not yet received it. The mailbox rule has been adapted to include electronic communications such as email and fax, and it varies across different states and jurisdictions. However, it does not apply to option contracts, where acceptance is only effective when received by the offeror. The common law mailbox rule has also been impacted by regulations such as Sec. 7502, which addresses the issues caused by the physical-delivery rule and provides exceptions for tax documents sent through registered or certified mail.
| Characteristics | Values |
|---|---|
| Name | Mailbox Rule, also called the Posting Rule |
| Application | A default rule in contract law |
| Purpose | Determining when an offer is accepted |
| History | Originated in the British case of Adams v. Lindsell (1818) |
| Offer Acceptance | An offer is considered accepted when the offeree places the acceptance in the mailbox, regardless of whether the offeror receives it |
| Communication Medium | Applicable to mail, fax, telegram, email, and other electronic communications |
| Exceptions | Option contracts, where acceptance is effective upon receipt |
| Circumstantial Evidence | Allows for testimonial and circumstantial evidence to prove timely mailing |
| Regulatory Status | Superseded by Sec. 7502 in some jurisdictions, but not all |
| Delivery Requirements | Proper addressing, adequate postage, and actual delivery |
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What You'll Learn
- The mailbox rule applies to bilateral contracts, not option contracts
- Acceptance is effective on dispatch, rejection on receipt
- Offerors bear the risk of delays or failures in the mail system
- The mailbox rule originated in Adams v. Lindsell (1818)
- The rule has been adapted to include electronic communications

The mailbox rule applies to bilateral contracts, not option contracts
The mailbox rule, also known as the "postal rule" or "deposited acceptance rule", is a rule in contract law that determines when an offer is accepted. It states that an offer is considered accepted as soon as the offeree communicates their acceptance, whether by mail, email, fax, telegram, or any other means of communication. This means that acceptance is effective on dispatch, even before the offeror has received it.
However, it is important to note that the mailbox rule does not apply to all types of contracts. In particular, the mailbox rule applies to bilateral contracts but not to option contracts. A bilateral contract is a contract in which both parties make promises to each other. On the other hand, an option contract gives the holder the right, but not the obligation, to buy or sell an asset at a predetermined price.
The distinction between bilateral contracts and option contracts in the context of the mailbox rule is important. Under the mailbox rule, an acceptance of a bilateral contract is considered effective as soon as it is dispatched and is out of the offeree's possession, regardless of whether it ever reaches the offeror. This is because the mailbox rule assumes that when one makes an offer through a particular medium, they authorize the acceptance to be made through the same medium.
However, for option contracts, the mailbox rule does not apply. In the case of option contracts, acceptance is only effective upon receipt by the offeror. This means that even if the offeree communicates their acceptance by dispatching a letter or email, the contract is not considered accepted until the offeror receives the acceptance. This distinction is crucial in understanding the application of the mailbox rule and has been established in various state laws and court cases.
It is worth noting that there are some exceptions to the general rule. For example, in California, the mailbox rule also applies to option contracts. This means that if an offeree exercises their option by sending a letter or email, the contract is considered accepted as soon as the letter is dispatched or the email is sent, even if the offeror has not received it yet. Additionally, parties to a contract can agree to contract around the mailbox rule and determine for themselves at what time an offer will be considered accepted.
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Acceptance is effective on dispatch, rejection on receipt
The mailbox rule, also known as the posting rule, is a default principle in contract law that determines the time at which an offer is accepted. The rule states that an offer is considered accepted as soon as the offeree dispatches their acceptance, regardless of whether the offeror has received it. This can be done through any reasonable means of communication, such as mail, fax, telegram, or email, as long as it is irrevocable once sent. This rule provides clarity and certainty in contract formation, allowing offerees to rely on the formation of a contract once they have dispatched their acceptance. It also protects offerees by ensuring that their acceptance is effective immediately, even if there are delays or issues in delivery.
However, it is important to note that the mailbox rule does not apply in all cases. Firstly, it only applies to bilateral contracts and not to option contracts, where acceptance is only effective upon receipt by the offeror. Additionally, parties can contract around the mailbox rule by stipulating different terms for acceptance in their agreements. For example, they can specify that acceptance is only effective upon receipt rather than dispatch.
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, even though the offeror had not yet received it. This rule has been adapted to include electronic communications, and courts may apply similar principles to determine when acceptance occurs in digital contexts.
While the mailbox rule provides a predictable framework for contract formation, it also raises some interesting questions. For example, what happens if an offeree mails both an acceptance and a rejection to the offeror? According to the mailbox rule, if an acceptance is mailed before a rejection, a valid contract is formed, even if the offeror receives the rejection first. However, if the offeror receives and relies on the rejection before receiving the acceptance, a contract cannot be enforced.
In the United States, the common law mailbox rule has been the subject of debate, particularly in tax-related cases. In 1954, Congress enacted Sec. 7502, which provided criteria for the timely filing of tax documents. Some courts held that Sec. 7502 superseded the common law mailbox rule, while others argued that it only provided a safe harbor, and the common law mailbox rule could still be applied. To resolve this split, the IRS issued regulations in 2011, clarifying that the common law mailbox rule was abolished and that Sec. 7502 provided the exclusive means to establish prima facie evidence of document delivery.
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Offerors bear the risk of delays or failures in the mail system
The common law mailbox rule is a long-standing principle in contract law that determines when an offeror's acceptance of an offer is effective and when it is communicated to the offeree. The rule states that acceptance of an offer is effective when the acceptance is placed in the mail, rather than when it is received by the offeror. This means that the risk of loss or delay in the mail system rests with the offeror, not the acceptor.
The mailbox rule is based on the idea that once an acceptor places their acceptance in the mail, they have done all that they can do to complete the acceptance and are no longer in control of the situation. The acceptance is deemed to be 'out of the acceptor's hands' and thus they should not bear the risk of any subsequent delays or failures in the mail system.
This rule is particularly important in common law jurisdictions, where it forms a key part of contract law. It provides certainty and clarity to parties entering into contracts, as it establishes a clear point at which acceptance is effective. Without this rule, there could be significant uncertainty as to whether an acceptance had been effectively communicated, particularly in situations where mail services are unreliable or subject to delay.
Therefore, offerors must bear the risk of any delays or failures in the mail system. This means that if an acceptance is lost, delayed, or misdirected in the mail, the offeror is still bound by the contract. The rule encourages offerors to consider the reliability of the mail system when making offers and to allow for sufficient time for acceptance to be communicated. It also incentivizes offerors to choose more reliable methods of communication if they require certainty and speed in the acceptance process.
It is worth noting that the mailbox rule can be displaced by contrary agreement between the parties. For example, they may specify that acceptance is only effective upon actual receipt or through the use of specific communication methods. Additionally, the rule may not apply in situations where the offeror has specified a particular form of acceptance, such as requiring a signed contract to be returned, or where immediate notification of acceptance is essential to the contract.
In conclusion, the common law mailbox rule allocates the risk of delays or failures in the mail system to the offeror. This rule provides certainty in contract law and encourages offerors to consider the reliability of their chosen communication methods. While the rule can be displaced by contrary agreement or specific requirements in the offer, it remains a fundamental principle that shapes the formation of contracts and the allocation of risk between parties.
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The mailbox rule originated in Adams v. Lindsell (1818)
The mailbox rule, also known as the posting rule, is a default rule in contract law that determines when an offer is accepted. The rule states that an offer is considered accepted as soon as the offeree sends their acceptance, rather than when the offeror receives it. This rule applies to various means of communication, such as mail, fax, telegram, or email, as long as the acceptance is irrevocable once sent.
The mailbox rule originated in the British case of Adams v. Lindsell in 1818. In this case, the defendants, wool dealers, sent a letter to the plaintiffs, wool manufacturers, offering to sell them fleeces. The defendants specified that they would await acceptance of their offer through the mail. The plaintiffs mailed their acceptance within a reasonable time frame, but the defendants did not receive it until a few days later, during which they sold the wool to someone else.
The Court of King's Bench upheld the trial court's ruling that the acceptance was valid from the time the acceptance letter was mailed. This decision established the mailbox rule, which states that when an offer is made via mail, acceptance is complete upon mailing, even before the offeror receives it. The court determined that the buyer accepted the seller's offer when they responded, regardless of when the seller received the reply.
The mailbox rule is a default rule, and parties to a contract can choose to opt-out or modify the terms of their agreement. It is important to note that the mailbox rule may vary from state to state, and it does not apply to all cases. Additionally, the offeror can specify the particular means of acceptance, and if the offeree uses a different method, the acceptance may be invalid, and the mailbox rule will not apply.
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The rule has been adapted to include electronic communications
The common-law mailbox rule, also known as the posting rule, is a default rule in contract law that determines when an offer is accepted. The rule states that an offer is considered accepted the moment the offeree mails their letter, rather than when the offeror receives it. This rule was established in the British case of Adams v. Lindsell (1818), where the Court decided that the buyer accepted the seller's offer when they responded, not when the seller received the reply.
The mailbox rule has been adapted to include electronic communications. In an increasingly digital world, the Uniform Electronic Transactions Act (UETA) § 15, adopted by 47 states and territories, has modified the mailbox rule for electronic communications. The UETA requires that electronic records be properly addressed or directed to the recipient's information processing system and that the recipient can retrieve the record. This ensures that contractual information sent electronically is received by the intended party and can be accessed and processed by their system.
The application of the mailbox rule to electronic communications raises some interesting considerations. For example, "do-not-reply" email addresses and shared inboxes can create issues. "Do-not-reply" emails bounce back to the sender without reaching the intended recipient, while shared inboxes may allow for the interception or deletion of messages by unintended parties. Therefore, it is generally not recommended to send contractual information to a shared inbox.
Additionally, the mailbox rule states that for an acceptance to be effective upon dispatch, it must be sent in a timely and proper manner. This includes using an appropriate medium of communication. While email is now an acceptable medium, certain types of email communications, such as encrypted emails, may not transmit properly or may be unopenable by the recipient. Therefore, when sending contractual information electronically, it is essential to ensure that the recipient's system can process the communication and that the recipient can access it.
The mailbox rule does not apply to option contracts, where acceptance is only effective when received by the offeror. Furthermore, the rule can be superseded by specific instructions from the offeror regarding the means of acceptance. If the offeror specifies a particular method of acceptance, such as via fax, any other form of acceptance will be invalid. However, if no specific instructions are given and the offeree uses an unreasonable means of acceptance, the acceptance may still be valid, but the mailbox rule will not apply, and acceptance will only be effective upon receipt.
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Frequently asked questions
The mailbox rule, also called the posting rule, is the 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 places their acceptance in the mailbox, regardless of whether the offeror has received it.
For the mailbox rule to apply, the acceptance must be sent in a timely and proper manner. The offeree must respond within a reasonable time period, and the acceptance must be properly addressed with sufficient postage.
No, the mailbox rule does not apply to option contracts. In these cases, the acceptance is only effective when it is received by the offeror.
The mailbox rule has been adapted to include electronic communications such as email, fax, and other digital means. Courts apply similar principles to determine when acceptance occurs in these electronic contexts.
Yes, in 1954, Congress enacted Sec. 7502, which addresses the physical-delivery rule. Some courts have held that this supersedes the common law mailbox rule, while others consider it supplemental. The IRS also issued regulations in 2011 to clarify that Sec. 7502 provides the exclusive means to establish evidence of document delivery.











































