28 CFR 540.19 - Legal correspondence.
(a) Staff shall mark each envelope of incoming legal mail (mail from courts or attorneys) to show the date and time of receipt, the date and time the letter is delivered to an inmate and opened in the inmate's presence, and the name of the staff member who delivered the letter. The inmate may be asked to sign as receiving the incoming legal mail. This paragraph applies only if the sender has marked the envelope as specified in § 540.18.
(b) The inmate is responsible for advising any attorney that correspondence will be handled as special mail only if the envelope is marked with the attorney's name and an indication that the person is an attorney, and the front of the envelope is marked “Special Mail - Open only in the presence of the inmate”. Legal mail shall be opened in accordance with special mail procedures (see § 540.18).
(c) Grounds for the limitation or denial of an attorney's correspondence rights or privileges are stated in part 543, subpart B. If such action is taken, the Warden shall give written notice to the attorney and the inmate affected.
(d) In order to send mail to an attorney's assistant or to a legal aid student or assistant, an inmate shall address the mail to the attorney or legal aid supervisor, or the legal organization or firm, to the attention of the student or assistant.
(e) Mail to an inmate from an attorney's assistant or legal aid student or assistant, in order to be identified and treated by staff as special mail, must be properly identified on the envelope as required in paragraph (b) of this section, and must be marked on the front of the envelope as being mail from the attorney or from the legal aid supervisor.