Is it illegal for the property to unlock the mailbox without authorization?

Illegal. The Property Law stipulates that it is illegal for a property to pry open the owner's mailbox lock without the owner's consent, which involves infringing on the owner's property rights and privacy rights. Privacy refers to a kind of personality right that citizens enjoy the peace of private life, and private information is protected according to law, and is not illegally harassed, informed, collected, used and made public by others.