Special mail also includes correspondence received from the following: President and Vice President of the United States, attorneys, Members of the U.S. Congress, Embassies and Consulates, the U.S. Department of Justice (excluding the Bureau of Prisons but including U.S. Attorneys), other Federal law enforcement officers, State Attorneys General, Prosecuting Attorneys, Governors, U.S. Courts (including U.S. Probation Officers), and State Courts. For incoming correspondence to be processed under the special mail procedures (see §§ 540.18-540.19), the sender must be adequately identified on the envelope, and the front of the envelope must be marked "Special Mail-Open only in the presence of the inmate".
28 C.F.R. § 540.2