(a) The matter described in subsection (b) of this section (other than matter mailed under section 3404 of this title) may be mailed free of postage, if—
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;
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;
the matter may be opened by the Postal Service for inspection; and
the matter contains no advertising.
(b) The free mailing privilege provided by subsection (a) of this section is extended to—
paper, records, tapes, and other material for the production of reading matter, musical scores, or sound reproductions;