The Inspector General recently issued a report on the use of mail covers to spy on mail. It found procedures were not being followed in a substantial number of cases. Politico reports:

The U.S. Postal Service failed to observe key safeguards on a mail surveillance program with a history of civil liberties abuses, according to a new internal watchdog report that USPS managers tried to keep secret, citing security concerns.

...The Office of Inspector General audit of so-called “mail covers” — orders to record addresses or copy the outside of all mail delivered to an individual or an address — found that about 20 percent of the orders implemented for outside law enforcement agencies were not properly approved, and 13 percent were either unjustified or not correctly documented.

The post office issued 40,000 mail covers last year. The postal inspectors didn't want the report made public, but the inspector general's office published a redacted version anyway. You can read it here.