mailman vs postman

mailman and postman both are nouns.

Word	Noun	Adjective	Verb	Adverb
mailman	Yes	No	No	No
postman	Yes	No	No	No

As nouns, mailman and postman are synonyms defined as:

Other synonyms of mailman include carrier, letter carrier, mail carrier.

mailman (noun)	postman (noun)
a man who delivers the mail	a man who delivers the mail