postman vs mailman

postman and mailman both are nouns.

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

As nouns, postman and mailman are synonyms defined as:

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

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