shall be paid by appropriations for the official mail costs of the Senate and the House of Representatives for that purpose and then paid to the Postal Service as postal revenue. Except as to Mailgrams and except as provided by sections
733 and
907 of title
44, envelopes, wrappers, cards, or labels used to transmit franked mail shall bear, in the upper right-hand corner, the sender’s signature, or a facsimile thereof.