In the 1913 case Little v. Williams, the United States Supreme Court ruled in favor of a postmaster who had been sued for refusing to deliver mail that he believed was being used for fraudulent purposes. The plaintiff, Mr. Little, operated a business selling shares in mining companies and claimed that his business was legitimate; however, Postmaster Williams refused to deliver his mail on suspicion of fraudulence based on complaints received from customers claiming they were defrauded by Mr. Little's company. The court held that under federal law at the time (the Act of March 2nd), postmasters had discretion to withhold delivery if they reasonably suspected mail was being used for illegal activities such as frauds or swindles - even without absolute proof of wrongdoing. This decision affirmed an important principle: postal officials have not only the right but also duty to protect public against schemes conducted through use of mails which are reasonably calculated to deceive and defraud public.

In the dissenting opinion for Little v. Williams, Justice Holmes disagreed with the majority's decision to overturn a conviction based on an error in jury instructions. He argued that while there was indeed an error made by the trial judge during his instruction to the jury, it did not necessarily mean that this mistake influenced or prejudiced their verdict against Little. The justice believed that such errors should only result in a reversal of judgment if they have likely affected the outcome of proceedings and led to substantial injustice. In this case, he felt there was no clear evidence indicating that without said error, Little would not have been convicted by jurors who were convinced beyond reasonable doubt about his guilt based on presented facts and testimonies.