What is the minimum thickness requirement for letter-size mail which is more than 4¼ inches high or 6 inches long?

The correct choice reflects the minimum thickness requirement set for letter-size mail that exceeds specific dimensions—more than 4¼ inches high or 6 inches long. According to postal regulations, mailpieces must meet certain thickness criteria to ensure they can be processed efficiently through the postal system. A minimum thickness of 0.009 inches is specified for such letters to avoid complications in sorting and handling. This thickness helps maintain the integrity and proper delivery of the mail, ensuring that it is neither too flimsy nor at risk of getting damaged during transit. Understanding these specifications is crucial for anyone involved in mailing practices to ensure compliance with postal service guidelines.