The mailbox rule raises interesting questions when the target recipient sends both an acceptance and a rejection to the provider. Again, the PO Box rule states that an acceptance with shipping and a rejection with the receipt are effective. If so, what happens when a target recipient decides to accept, then changes their mind and rejects or vice versa? If an acceptance is sent by mail before a rejection, a valid contract is concluded. Since acceptance is effective with shipment and rejection is effective upon receipt, a contract is concluded as soon as acceptance is stored in the post office. This also applies if the supplier first receives the rejection. For example: Rejection of a contract: The words or actions of a contracting party that indicate the intention not to perform the contract in the future. Alternatively, an unconditional refusal by a party to perform the actions prescribed in a contract. According to the display rule, the service is a means of acceptance. If A orders 1000 blue coats and B sends it, this shipment is considered a transmission of the acceptance of A`s offer to buy the hangers.
A defective performance is also an acceptance, unless a declaration is attached. For example, if A orders 1000 blue coathangers and B accidentally sends 1000 red coathangers, this is still a contract acceptance. However, if B sends the red coathangers a note they sent them because they ran out of blue coathangers, it is not an acceptance, but an accommodation which is a form of counter-offer. As a result, the beginnings of the postal rule arose, in which acceptance was described as effective with a few exceptions. However, the complete postal rule that acceptance is effective from the moment the letter of acceptance is duly abandoned will not be decided in Henthorn v. Fraser before 1892. Again, the crucial question is when the acceptance is sent, not when it is received by the supplier. If an acceptance is sent within a reasonable time, a valid contract has also been concluded if the supplier receives the acceptance after the expiry of the period. An example: A rule of contract law that is an exception to the general rule that an acceptance is made only if it is communicated directly to the supplier.
As mentioned earlier, this idea is codified by the “mailbox rule,” which states that acceptance is effective with shipping even before the vendor has received it. (The only small exception to this rule is option contracts, the assumptions of which are not effective until they have been received by the bidder.) See Cities Service Oil Co., v. National Shawmut Bank, 172 N.E.2d 104 (Mass. 1961). In 1818, Adams v. Lindsell began to clarify the law on the acceptance of tenders by determining when an offer was accepted and therefore when a binding contract was concluded. The case revolved around an offer to sell wool. As a result of an error in the orientation of the offer, acceptance was delayed and the supplier sold the wool to a third party. Further information on this and other cases, as well as on the postal rule, can be found under the heading “Offer and acceptance” in the Contract Law section. The rule was established by a series of cases from the 19th century. Starting with Adams v Lindsell (1818) B & Ald 681, which was later confirmed and expanded in Dunlop v Higgins (1848) 1 HL Cas 381, Household Fire and Carriage Accident Insurance Co Ltd v Grant (1879) 4 Ex D 216 and Henthorn v Fraser  2 Ch 27. If the customer places this acceptance in the mailbox for the return, even if it never reaches the supplier, the contract is deemed to have been concluded.
In order to be effective with shipping, acceptance must be timely and appropriate. With regard to speed, the target recipient must respond within a reasonable time if the provider does not specify an acceptance period. If a period is specified, the general rule is that the period begins to run when the target recipient receives the offer. For example: For more information on option contracts, check out this article in the Florida State University Scholarship Repository, this article in the California Law Review, and in this Indiana Law Journal article, Postal Rule is a Fundamental Rule of Offer and Acceptance in English Contract Law. It notes that the actual communication of acceptance by letter is made at the time of publication. Many jurisdictions call this the mailbox rule, but even in Canada there are disagreements: Waddams calls it in contract law the “mailbox rule; but Fridman, in The Law of Contract, on the “postal acceptance rule.” The booking rule only applies to acceptance. Other contract letters (such as . B withdrawal of the offer) take effect only after delivery of the letter, as in Stevenson, Jacques & Co v. McLean (1880) 5 QBD 346. As a result, it is possible that a letter of acceptance will be published after the publication of a letter of withdrawal of the offer, but before its delivery, and the acceptance will be complete at the time of publication of the letter of acceptance – the withdrawal of the supplier would be ineffective.
The general rule is that assumptions are effective with shipping (when shipped). .