Analysis of information sources in references of the Wikipedia article "Portmanteau (luggage)" in English language version.
A 1726 dictionary defines a portmanteau as a Mail or a Cloak Bag...
This style of bag, sometimes called a portmanteau, was used by the Post Office Department in the mid-1800s to transport mail...
In the 19th century, both newspapers and letters were placed in a portmanteau, a round, side-opening, leather bag.
It directed that here, All letters... are placed in a portmanteau [or] principal mail bag...
