transmitting vs mailing

transmitting and mailing both are nouns.

Word	Noun	Adjective	Verb	Adverb
transmitting	Yes	No	No	No
mailing	Yes	No	No	No

As nouns, mailing is a hyponym of transmitting; that is, mailing is a word with a more specific, narrower meaning than transmitting:

transmitting: the act of sending a message; causing a message to be transmitted
mailing: the transmission of a letter

Other hyponyms of transmitting include forwarding, posting, telephotography.

transmitting (noun)	mailing (noun)
the act of sending a message; causing a message to be transmitted	the transmission of a letter
	mail sent by a sender at one time