Don’t list PBL hits.. that’s meaningless. It just means the IP is a “home” computer and shouldn’t be running a mail server or sending mail. But posting a message on Discourse is not sending an email, that’s just using a web browser, which a home IP address can definitely be doing.
http://www.spamhaus.org/pbl/query/PBL1546707
This IP address range has been identified by Spamhaus as not meeting our policy for IP addresses permitted to deliver unauthenticated ‘direct-to-mx’ email to PBL users.