According to federal law, Postal Service employees are mandated to _____ and _____ all mail placed in its ____.

The correct answer highlights the responsibilities that Postal Service employees hold in relation to mail. According to federal law, Postal Service employees are mandated to preserve and protect all mail placed in its custody.

This emphasizes the critical role of ensuring that all mail is handled with care and security, preventing loss, theft, or damage to the mail. Preservation ensures that items are kept in a suitable condition and are not subject to decay or deterioration, while protection involves safeguarding the mail against unauthorized access and potential harm.

In the context of the United States Postal Service, the use of the term "custody" specifically refers to the duty of care that postal employees have over the mail once it is in their possession. This legal obligation reflects the trust placed in these employees by the public and the importance of the postal service as a reliable means of communication and delivery.

The other choices, while they may suggest related responsibilities, do not capture the specific legal obligations set forth in federal law regarding the handling of mail.