send vs mail out

send and mail out both are verbs.

Word	Noun	Adjective	Verb	Adverb
send	No	No	Yes	No
mail out	No	No	Yes	No

As verbs, mail out is a hyponym of send; that is, mail out is a word with a more specific, narrower meaning than send:

send: to cause or order to be taken, directed, or transmitted to another place
mail out: transmit by mail

Other hyponyms of send include send in, get off, mail.

send (verb)	mail out (verb)
cause to be directed or transmitted to another place	transmit by mail
transfer
broadcast over the airwaves, as in radio or television
assign to a station
to cause or order to be taken, directed, or transmitted to another place
transport commercially
cause to go somewhere
cause to be admitted; of persons to an institution