为亚当斯五世素邮政规则数的理由是由Ewan McKendrick在他的书中讨论的，“合同法”。首先，有人认为，邮局作为一个受要约人的代理人，因此一旦信接受代理，这是接受有效的沟通。[ 2 ] McKendrick说，这是开放的辩论，因为邮局显然没有明示授权合同对受要约人的代表。[ 3 ]其次，有人认为，要约人选择启动谈判后，则要约人必须承担的有关合同文件邮寄相关的所有责任。然而，这个理由已经由Hentnorn V弗雷泽决策带来的问题，[ 4 ]，认为它是合理利用邮政邮政规则仅适用于。为探讨究竟McKendrick，构成合理的情况下使用后的问题是值得商榷的，例如，在双方生活重要的距离彼此可以合理使用，但它是没有必要启动谈判后通过。[ 5 ]会的，因此，不太可能这样的一个理由是能够依靠的；有不确定性，当它成为合理使用后。一个更为坚实的理由是，受要约人应能够信赖他或她已将接受的事实，因此满足了他或她的程序责任的规则下形成的合同。McKendrick说，一个更好的方式在这个理由光看邮政的规则是，一旦封贴，要约不能撤销其要约，而不是承诺生效一次信已经寄出。[ 6 ]这地方的责任落在了要约，受要约人有遵守在接受他提供所需的所有合理要求。然而，一般的规则讨论亚当斯做了进一步的阐述和盘踞在家庭火灾和运输事故保险有限公司诉给后者。[ 7 ]在这种情况下，认为通过要约生效后，一旦被人贴，不在接受受要约人打开。这进一步加强了的理由，它是要约人的责任，允许任何延迟或潜在的邮局对于任何合同谈判由后。
A number of justifications for the postal rule of Adams v Lindsell are discussed by Ewan McKendrick in his book, ‘Contract Law’. Firstly, it is argued that the Post Office acts as an agent of the offeree, and hence once the letter is received by an agent, this constitutes valid communication of acceptance. McKendrick says that this is open to debate, given that the Post Office clearly has no express authority to contract on behalf of the offeree. Secondly, it is argued that given the offeror has chosen to initiate negotiations by post, then the offeror must bear all responsibility associated with the postage of documents relating to the contract. However, this justification has been brought into question by the decision in Henthorn v Fraser, where it was held that the postal rule only applies where it is reasonable to use the post. As McKendrick discusses, the issue of what exactly constitutes a reasonable situation to use the post is questionable, for example, where two parties live a significant distance from one another it may be reasonable to use the post, however it is not necessary to initiate negotiations through the post. It would, therefore, be unlikely that such a justification could be relied upon; given there is uncertainty as to when it becomes reasonable to use the post. A more solid justification is that an offeree should be able to rely upon the fact that he or she has posted the acceptance, and hence has satisfied his or her procedural duties under the rules governing the formation of a contract. McKendrick says that a better way of viewing the postal rule in light of this justification is that, once the letter is posted, the offeror cannot revoke his offer, rather than the acceptance taking effect once the letter has been sent. It places the onus squarely on the offeror, given that the offeree has complied with all reasonable requests required of him in accepting the offer. However, the general rule discussed in Adams was further elaborated upon and entrenched in the later case of Household Fire and Carriage Accident Insurance Co Ltd v Grant. In this case, it was held that an acceptance of offer communicated by post becomes valid once it has been posted by the offeree, not when it is received and opened by the offeror. This further strengthens the justification that it is the responsibility of the offeror to allow for any delays or mishandlings by the Post Office in regards to any contractual negotiations conducted by post.