When you drop a letter in a public mailbox, you expect it to reach its destination safely and in good condition. Before 1891, people using the U.S. mail couldn't make those kinds of assumptions. Public mailboxes were semi-open, which made it easy for thieves to steal mail and for elements like rain and snow to damage letters. Philip B. Downing changed that with a mailbox design that featured an outer door and an inner safety door. When the outer door was open, the safety door remained closed so the mail was safe from thieves and inclement weather. When the outer door closed, the safety door would open so that the deposited mail would join the other letters in the box. This safety device was the precursor for the public mail boxes we see today.