/pō-stiŋ/
n. Noun corresp. to v. post (but note that post can be nouned). Distinguished from a 'letter' or ordinary email message by the fact that it is broadcast rather than point-to-point. It is not clear whether messages sent to a small mailing list are postings or email; perhaps the best dividing line is that if you don't know the names of all the potential recipients, it is a posting.