post ‧ bag /ˈpəʊstbæɡ $ ˈpoʊst-/ BrE AmE noun British English
1 . [singular] all the letters received by an important person, television programme etc on a particular occasion:
We’ve had an enormous postbag on the recent programme changes.
2 . [countable] a bag for carrying letters, used by the person who delivers them SYN mailbag American English