The United States Postal Service has some convenience features which may or may not be secure. I have my doubts.
The first feature is Informed Delivery. You can sign up for free, and then every day you receive an email that has scans of the envelopes you will receive that day. It’s a nice feature when you are eagerly awaiting a certain letter, like an automobile registration or a license.
However, it is relatively easy to sign up and have your identity verified. It occurred to me that someone could impersonate you, and sign up. The could watch the daily emails, and if you have a rural free delivery mailbox, they could swoop in and steal anything that appeared interesting.
I believe the identity verification required a credit card, but the bad guys would find that relatively simple to circumvent.
On top of everything else, the USPS in monetizing this. Informed delivery has crazy high open rates for that email, and gives a traditional mail marketer a lot more information about you, and new tools to get you interested in their products. Read about it here.
Whatever, my recommendation is you sign up for informed delivery before someone does it for you.