28 C.F.R. § 540.16 – Inmate correspondence while in segregation and holdover status.

(a) The Warden shall permit an inmate in holdover status (i.e., enroute to a designated institution) to have correspondence privileges similar to those of other inmates insofar as practical.
(b) The Warden shall permit an inmate in segregation to have full correspondence privileges unless placed on restricted general correspondence under § 540.15.