After the mail had been removed from the catch bar, it was dumped on the table in the center of the car. On this table the clerks sorted the mail and deposited it in the appropriate canvas mail bags hung on the rows of hooks on the inside walls of the car. Other mail was put in the appropriate mail slot on the middle wall of the car.
Mail Express 7815 was owned and maintained by the railway, but the mail clerks were employed by the Canadian Postal Service. Between 4 and 10 mail clerks worked this car in shifts. At the end of their shift they got off at various stations and were replaced with other clerks, so that mail could be sorted around the clock as the train moved across the country. The C.N.R. could guarantee letters from Montreal to Vancouver in four days.
There is a small doorway between the mail section and the express section. It was kept locked, and only opened when parcels or mail had to be passed from one side to the other.
The express section had between one and five expressmen working in it. Valuables and company payrolls were shipped by train, so the car doors on the express section were kept locked and only opened at the larger city stations, where armed guards were used to protect the car’s contents. Sometimes, armed guards even traveled inside the car.
There is also a mail slot near the middle of the car. If this car was stopped in a station, you could drop your mail into the slot to be sorted en route.
Mail in Canada went by train until 1970, when Canada Post began sending mail by plane and truck.
For more detailed information see: http://en.wikipedia.org/wiki/Railway_post_office