"Notmuch is not much of an email program. It doesn't receive messages (no POP or IMAP support). It doesn't send messages (no mail composer, no network code at all)."

notmuch doesn't replace mutt, you use it with mutt/offlineimap etc as your mail indexer, which makes massive mail archives instantly searchable.. (and does this extremely well)

I suspect this what the grandparent was referring to, it's not intended as a mutt replacement, so to complain that it doesn't replace it well is a bit unfair