Due to the well-known crappiness of the Oracle autoresponders, which send spam to public lists, for the lists I am moderator of I not only reject autoreplies but blacklist the sender, using the fourth link offered in the moderator's notification mail. (Who knows how long it will be before the sender gets back to work, and in some cases they have never even posted a real message anyway.) But messages keep coming in to the moderator from the same sender even though they were supposedly blacklisted.
I can confirm that blacklisting does not work.
In list firstname.lastname@example.org we recently blacklisted user spamming the list, but it does not have any effect.
I am raising priority. This is real issue. We do not have moderator's manpower for setting any more lists as moderated.
Should work better now.
Still does not work. See email@example.com's successful post  despite that address being blacklisted  a week earlier.
That user is actually subscribed to the list in question. And the current setup is to query the blacklist only after the subscriber-check.
Works as specified.