39 C.F.R. § 761.6
A Reserve Bank which has received Postal Service securities and effected pledges, made entries regarding them, or transferred or delivered them according to the instructions of its depositor is not liable for conversion or for participation in breach of fiduciary duty even though the depositor had no right to dispose of or take other action in respect of the securities. A Reserve Bank shall be fully discharged of its obligations under this part by the delivery of Postal Service securities in definitive form to its depositor or upon the order of such depositor. Customers of a member bank or other depositary (other than a Reserve Bank) may obtain Postal Service securities in definitive form only by causing the depositor of the Reserve Bank to order the withdrawal thereof from the Reserve Bank.
39 C.F.R. § 761.6