Code sections cited in this answer are to the New Mexico Criminal code, Chapter 30 as they were in my answer to the linked question, and to chapter 59A.
Neither the landlord (whom I will cal LL) , nor any ordinary citizen, is legally required to report information that s/he may have about a crime to the police or other authorities. LL cannot actively conceal ...
The Postal Services Act 2000 does not allow you to delay someone else's post:
84 Interfering with the mail: general.
(1) A person commits an offence if, without reasonable excuse, he—
(a) intentionally delays or opens a postal packet in the course of its transmission by post ...
Section 125(3)(a) defines "transmission by post":
renting a single room with three other guys each renting their own rooms
means exactly what it says.
What you are paying for is that room, plus shared access to the common areas.
Without knowing exactly what your lease says, especially with respect to the common areas, it's difficult to give a proper answer.
I suspect that the lease for your room says ...