pouch vs mail pouch

pouch and mail pouch both are nouns.

Word	Noun	Adjective	Verb	Adverb
pouch	Yes	No	Yes	No
mail pouch	Yes	No	No	No

As nouns, mail pouch is a hyponym of pouch; that is, mail pouch is a word with a more specific, narrower meaning than pouch:

Other hyponyms of pouch include mailbag, pocket, sporran, tobacco pouch, belt bag, waist pack.

pouch (noun)	mail pouch (noun)
a small or medium size container for holding or carrying things	pouch used in the shipment of mail
(anatomy) saclike structure in any of various animals (as a marsupial or gopher or pelican)
an enclosed space

pouch (verb)	mail pouch (verb)
swell or protrude outwards
put into a small bag
send by special mail that goes through diplomatic channels