Njabl.org Rejections

As of Jan 02/2019, the domain name njabl.org was set to expire and DNS servers were switched to Tucows autorenew servers which would cause any lookups by servers still not having removed the configuration to have rejections.

Remove any blacklistings regarding njabl.org from your servers in order to prevent this from occurring - and since your mail is being filtered, there should be no need to any have additional filtering set on your server.

https://en.m.wikipedia.org/wiki/Not_Just_Another_Bogus_List