Monday June 6th 2011@3:54pm ( moreinfo on laws concerning mail tampering)

If you have
intentionally opened it, with malice, then it is a federal offense, The
offenses are cited below, depending on the circumstances. Many times, I
am guilty of it too, we recieve an article through the mail and open it
before we realize that it is addressed to someone else. In these
cases, returning it to the Post Office and explaining that the mail
article was misdirected and you opened it in error- they will simply
resend it to the addressee with an apology for their mistake. Not only
that, but it is usually the addressee that will persue charges if they
believe their mail privacy has been violated.
I guess it just really depends on the circumstances invovled to give you a specific answer.
Hope these help. The web site is cited below if you would like further
details and these are statutes from the United States Codes (Federal Law
Register).
Sec. 1702. – Obstruction of correspondence

Whoever takes any letter, postal card, or package out of any post office
or any authorized depository for mail matter, or from any letter or
mail carrier, or which has been in any post office or authorized
depository, or in the custody of any letter or mail carrier, before it
has been delivered to the person to whom it was directed, with design to
obstruct the correspondence, or to pry into the business or secrets of
another, or opens, secretes, embezzles, or destroys the same, shall be
fined under this title or imprisoned not more than five years, or both

Sec. 1705. – Destruction of letter boxes or mail

Whoever willfully or maliciously injures, tears down or destroys any
letter box or other receptacle intended or used for the receipt or
delivery of mail on any mail route, or breaks open the same or willfully
or maliciously injures, defaces or destroys any mail deposited therein,
shall be fined under this title or imprisoned not more than three years

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