Defects in the devices used for transmitting messages are external, and usually not within the control
of the parties engaged in communication. The telephone, the postal system, the courier service, or
electronic media may fail. Messages can get delayed, distorted and even lost while being transmitted.
A partial failure of the mechanical equipment is more harmful than a total failure because a partial
failure may carry an incomplete or distorted message. A fax message can be wrongly delivered as a
wrong number can get dialled on the telephone. The printout may not be clear at all. It is advisable
to call up and check that the fax has been received.