It’s an adjective and it means not having or lacking enthusiasm. If someone is unenthusiastic about something it means they are feeling indifferent, apathetic, passive, phlegmatic, lukewarm, listless, languid, lethargic, emotionless, perfunctory about it.
The assumption is that all involved heard/read what was said (as would usually be the case on small Usenet newsgroups), all agreed upon it enough not to object, and no one had any objections, so the statement is presumed to have been heard and acknowledged.