Upon receipt of the official ballot, the registered voter shall mark it, seal the ballot in the identification envelope supplied with the ballot, sign the identification envelope, and comply with the instructions provided with the ballot. The voter may return the ballot to the election commissioner or county clerk by mailing it or by personally delivering it to the office of the election commissioner or county clerk. The deadline for receipt of the ballot is 5 p.m. on the date set for the election. The official ballot must be returned in the identification envelope. The registered voter shall, by signing the envelope, certify to the facts contained on the envelope. The election commissioner or county clerk shall keep the identification envelopes received from registered voters unopened in a fireproof safe or other suitable location which is locked until delivered to the counting board.