((a)) The matter described in subsection (b) of this section (other than matter mailed under ) may be mailed free of postage, if—

((1)) the matter is for the use of the blind or other persons who cannot use or read conventionally printed material because of a physical impairment and who are certified by competent authority as unable to read normal reading material in accordance with the provisions of sections 135a and 135b of title 2;

((2)) no charge, or rental, subscription, or other fee, is required for such matter or a charge, or rental, subscription, or other fee is required for such matter not in excess of the cost thereof;

((3)) the matter may be opened by the Postal Service for inspection; and

((4)) the matter contains no advertising.

((b)) The free mailing privilege provided by subsection (a) of this section is extended to—

((1)) reading matter and musical scores;

((2)) sound reproductions;

((3)) paper, records, tapes, and other material for the production of reading matter, musical scores, or sound reproductions;

((4)) reproducers or parts thereof, for sound reproductions; and

((5)) braille writers, typewriters, educational or other materials or devices, or parts thereof, used for writing by, or specifically designed or adapted for use of, a blind person or a person having a physical impairment as described in subsection (a)(1) of this section.