Mail which may be contaminated with a biotoxin, such as Anthrax, is received in a preliminary sorting area (16) including a dirty side sorting room (40) that is sealed to the ambient environment. The mail is loaded into a pass-through decontamination system (22) in which the mail is sterilized or otherwise decontaminated. The mail is removed from the pass-through system in a second or clean room (18) which is isolated from the first. The mail is then sorted and processed in the lean room (18). In the event that the sorting room (40) becomes contaminated or is suspected of being contaminated by pathogenic biological or chemical agents, a spray system (86) supplies a decontamination gas into the preliminary sorting area (16) to decontaminate the dirty side sorting room (40), any equipment (42, 44) in the room, and any mail located in the room.