In the United States v. Ramsey et al., 1925, the Supreme Court ruled that a warrantless search and seizure of international mail at U.S borders was not in violation of the Fourth Amendment's prohibition against unreasonable searches and seizures. The case arose when federal customs officials intercepted letters containing lottery tickets sent from abroad to addresses within the United States without obtaining a search warrant beforehand. The defendants argued this violated their Fourth Amendment rights, but Justice William Howard Taft wrote for an unanimous court that such searches were reasonable due to national sovereignty considerations and therefore did not require warrants. This decision established what is known as "border search exception" which allows for routine inspections and searches at points of entry into the country without violating constitutional protections.

In the dissenting opinion for United States v. Ramsey et al., Justice Holmes argued that the defendants should not have been convicted because they were unaware of their actions' illegality. He believed that a person could only be found guilty if they knowingly violated the law, and in this case, there was no evidence to suggest that Ramsey and his co-defendants knew their actions were illegal. Furthermore, he questioned whether it was fair to punish someone for unknowingly breaking an obscure law when even legal experts struggle to understand its complexities. Thus, he disagreed with the majority's decision to uphold the convictions based on what he saw as insufficient proof of intent.