mailing-card vs postal card

mailing-card and postal card both are nouns.

Word	Noun	Adjective	Verb	Adverb
mailing-card	Yes	No	No	No
postal card	Yes	No	No	No

As nouns, mailing-card and postal card are synonyms defined as:

mailing-card and postal card: a card for sending messages by post without an envelope

Other synonyms of mailing-card include post card, postcard.

mailing-card (noun)	postal card (noun)
a card for sending messages by post without an envelope	a card for sending messages by post without an envelope