a man who delivers the mail
"The friendly mailman waved as he walked down the street delivering letters to every house on his route."
someone (implied male) who delivers mail to, and/or collects mail from, residential or commercial addresses, or from public mailboxes
"The friendly mailman stopped at every door on our street to collect the outgoing letters."
In plain English: A mailman is a person who delivers letters and packages to houses for you.
"The mailman delivered our package while we were at work."
Usage: Use the gender-neutral term postal worker when referring to anyone delivering mail regardless of sex. Reserve "mailman" specifically for contexts where you are explicitly describing a male carrier.
The word mailman is a straightforward compound formed by combining mail and man. It was first used to describe the person responsible for delivering letters and packages.