posting vs transmittal

posting and transmittal both are nouns.

Word	Noun	Adjective	Verb	Adverb
posting	Yes	No	No	No
transmittal	Yes	No	No	No

As nouns, transmittal is a hypernym of posting; that is, transmittal is a word with a broader meaning than posting:

posting: the transmission of a letter
transmittal: the act of sending a message; causing a message to be transmitted

Other hypernyms of posting include transmission, transmitting.

posting (noun)	transmittal (noun)
the transmission of a letter	the act of sending a message; causing a message to be transmitted
a sign posted in a public place as an advertisement
(bookkeeping) a listing on the company's records