In the United States, mailboxes are considered federal property and federal law prohibits people from stealing, obstructing, or tampering with postal mail.  It is illegal to look in someone's mailbox or put something in it without violating federal law.

The United States Postal Service (USPS) offers a service called Informed Delivery where a resident can get a daily email with the scanned images of what is about to be delivered that day in the mailbox.  The USPS has a process for confirming a resident's address when they sign up for Informed Delivery but they do not have a process for deactivating people from an address once they move (if the person doesn't forward their mail) and they do not have a law that requires someone to deactivate their account when they move. It should be illegal to continue to access Informed Delivery for an address where someone no longer resides. If it is illegal to go to a mailbox and open it to see what was delivered, it should also be illegal to get Informed Delivery for that address. 

Allowing people to virtually sneak peek into someone's mailbox is a violation of that person's privacy. Informed Delivery should have the same protections that the physical mail in the mailbox has. This issue is especially important for women who get divorced and keep the "marital home," because their ex-husbands may be able to spy, stalk, and otherwise know personal information about them that may put them at risk for harm.

This is a BIPARTISAN issue. If it is illegal to touch the mailbox contents for a property that is not yours, it should be illegal to access Informed Delivery for an address where you no longer reside.  The USPS must change their processes and Congress should act immediately to add protections to Informed Delivery.