Mail Company v. Flanders was a United States Supreme Court case that dealt with the issue of whether a contract between a mail company and a postmaster was valid. The mail company had contracted with the postmaster to deliver mail to a certain location, but the postmaster had failed to do so. The mail company sued the postmaster for breach of contract. The Supreme Court held that the contract between the mail company and the postmaster was valid and enforceable. The Court found that the postmaster had a duty to perform the services he had agreed to, and that the mail company had a right to expect that the postmaster would fulfill his obligations. The Court also held that the mail company was entitled to damages for the breach of contract. The Court's decision in this case established that contracts between mail companies and postmasters were valid and enforceable. This decision has been cited in numerous other cases involving contracts between mail companies and postmasters. It is an important precedent in contract law and has been used to support the validity of contracts between mail companies and postmasters.

In the case of Mail Company v. Flanders, the Supreme Court was asked to decide whether a contract between two parties could be enforced if it had been made without consideration. The majority opinion held that such contracts were not enforceable because they lacked consideration and thus did not meet the requirements for an enforceable agreement under common law. However, in his dissenting opinion Justice Field argued that there should be no requirement of consideration when enforcing a contract as long as both parties agreed to its terms and conditions in good faith. He reasoned that requiring consideration would lead to injustice by allowing one party who has acted in bad faith or fraudulently to escape liability simply because their promise was unsupported by any form of compensation or benefit from the other party. Furthermore, he noted that courts have historically recognized certain types of agreements even without considerations being exchanged so long as both sides intended them to be binding on each other at the time they were entered into. Thus, Justice Field concluded that contracts lacking considerations should still be enforced according to their terms provided all other elements necessary for an enforceable agreement are present