在英国普通法上，要约人接受邮政通讯必须是“合理的”。在这种情况下，权威是Hentnorn V弗雷泽，[ 14 ]涉及原告交书面要约出售财产，他被告，而被告十四天的答辩。原告试图通过写信向被告撤回他们的提议，但是在被告已经将他们的接受信寄来后，这一撤销就到来了。它是由法院认为仍有有效的合同，鉴于双方居住在不同的和遥远的城镇，它将是合理的假设，被告会回复后提供的，因此它会一直在理解当事人的邮政规则将适用于合同的形成。在实际应用这方面的现代背景下，它将直接关系到任何谈判，通过电子邮件沟通，例如。如果协商是通过电子邮件开始的，那么假设接受将通过电子邮件回复是合理的。现代技术似乎不允许合理地理解邮政的使用，除非某种形式的谈判是通过邮寄方式进行的，或者要约人特别要求接受的是邮寄。虽然大量的通信仍然发生的后现代，它会出现，后使用的需要，在过去的一个世纪里下降，当邮政规则进行了介绍，由于替代的增加（瞬时）可用现代个人和企业通信手段。这意味着，在许多契约谈判中，合理的因素可能会妨碍邮政规则的生效，因为在许多情况下，它可能是不合理的（或必要的）使用邮政。
It has been established at English common law that it must be ‘reasonable’ for the offeror to accept that communication by post. The leading authority in this case is that of Henthorn v Fraser, which involved the plaintiff handing the defendant a written offer to sell property to him, with which the defendant had fourteen days to reply. The plaintiff sought to revoke their offer by writing to the defendant, however this revocation arrived after the defendant had already posted their letter of acceptance. It was held by the court that there was still a valid contract as, given that the two parties resided in different and distant towns, it would have been reasonable to assume that the defendant was going to reply to the offer by post, hence it would have been in comprehension of the parties that the Postal rule would apply at the formation of the contract. In terms of practically applying this to the modern context, it would directly relate to any negotiations that were communicated by email, for example. If a negotiation was commenced by email, then it would be reasonable to assume that the acceptance would be replied by email. Modern technology would appear to not allow for a reasonable comprehension of the use of post, unless some form of the negotiation was conducted by post, or the offeror specifically requested the acceptance be communicated by post. While a great deal of communication still takes place by post in modern times, it would appear that the need for the use of post has decreased over the course of the last century, when the Postal rule was introduced, due to the increase in alternative (and instantaneous) means of communication available to modern individuals and businesses. This means that the reasonableness factor may prevent the Postal rule from taking effect in many contractual negotiations, given that it may not be reasonable (or necessary) to use the post in many circumstances.