Good afternoon!
I believe what you are referring to is the limitations on postal rule, in regards to English contract law. The case that established this precedence is Adams v. Lindsell, which states that during a potential sales transaction, an acceptance of an offer by mail is complete as soon as the letter is put into the mailbox.
If this is the information you are looking for, to find solid references do an internet search on keywords such as "English postal rule", "Adams v. Lindsell", or "English contract law". Hopefully that will help you find what you need. If you do find some resources but are confused, please feel free to post them here and I will be more than happy to help you work through them.
I hope this helps you get started!
Regards,
Gloria
Moderator, EssayForum.com
Gloria, EssayForum.com