Section 50, The Public Procurement Act, 2004

(1) Subject to subsection (2) of section 28, a bid shall besubmitted in writing, duly signed and in a sealed envelope; and bids received after the deadline for submission of bids shall be returned unopened. (2) Invitation for prequalification and bidding documents shall permit submission of applications to prequalify or bids by hand or mail or by courier at the option of the bidder. (3) Subject to the policy laid down by the Authority, the bidding documents may authorise other methods of submission of bids, such as by electronic mail, as long as the confidentiality and security of bids are assured, including the prevention of the opening and reading of bids by anyone until the opening of bids at the time set in accordance with section 43. (4) Bids shall remain valid for the period of time indicated in the bidding documents, but modification or withdrawal of a bid during the bid validity period is subject to forfeiture of the bid security. (5) The validity period of a bid may be deemed extended only on the basis of the agreement of the bidder concerned and a bidder that agrees to an extension of the validity period of its bid shall also obtain a corresponding extension of the bid security, if such a security was required.