mailing (Noun) — Mail sent by a sender at one time. ex. "the candidate sent out three large mailings"
mailing (Noun) — The transmission of a letter. ex. "the postmark indicates the time of mailing"
mailing (Verb) — Send via the postal service. ex. "I'll mail you the check tomorrow"
mailing (Verb) — Give to a courier to take to another place. ex. "I'll mail you the paper when it's written"
mailing (Verb) — (computing) communicate electronically on the computer. ex. "she e-mailed me the good news"