0.0 RCVD_IN_ZEN_BLOCKED_OPENDNS RBL: ADMINISTRATOR NOTICE: The query to zen.spamhaus.org
was blocked due to usage of an
open resolver. ...
FYI: you'll need to run your own local resolver if you want to perform DNSBL queries with Spamhaus. Unbound (https://nlnetlabs.nl/) is an excellent and easy-to-configure choice for solving this problem.
Even running your own local resolver, if you generate enough traffic they'll still block you. I think their definition of open relay is based on traffic volume.
(which is their right, of course - just a warning that might help someone not find this out at 4am like I did)
Yes, because Spamhaus is a commercial enterprise. My own experience with their "free tier" limit is that it's generous and sufficient for personal use.
