28 C.F.R. § 540.13
When correspondence is rejected, the Warden shall notify the sender in writing of the rejection and the reasons for the rejection. The Warden shall also give notice that the sender may appeal the rejection. The Warden shall also notify an inmate of the rejection of any letter addressed to that inmate, along with the reasons for the rejection and shall notify the inmate of the right to appeal the rejection. The Warden shall refer an appeal to an official other than the one who originally disapproved the correspondence. The Warden shall return rejected correspondence to the sender unless the correspondence includes plans for or discussion of commission of a crime or evidence of a crime, in which case there is no need to return the correspondence or give notice of the rejection, and the correspondence should be referred to appropriate law enforcement authorities. Also, contraband need not be returned to the sender.
28 C.F.R. § 540.13