Running ISPConfig 3.2.8p1 on Ubuntu 20.04.5 LTS We have recently seen emails sent to our mailboxes in ISPConfig being bounced. The bounce error messages referred to spamhaus: Service unavailable; Client host [173.201.193.166] blocked using zen.spamhaus.org; Error: open resolver; https://www.spamhaus.org/returnc/pub/172.70.249.210and we had zen.spamhaus.org set as our Real-time Blackhole List (RBL) in ISPConfig (System > Server Config > Mail) as we always have. None of the bounced emails are listed in the RBL databases. It's a bit unclear but I think the zen.spamhaus.org service has been changed in some way ("Queries cannot successfully be made to the Spamhaus free infrastructure via public/open resolvers" - https://www.spamhaus.org/returnc/pub/) and Spamhaus are promoting a new service Spamhaus DQS). Is this true? To solve our problem we removed zen.spamhaus.org set as our RBL in ISPConfig and the email bounces stopped. However, we now have no RBL in place. Is there a recommended alternative to zen.spamhaus.org that plugs in without any customisation of the ISPConfig code? Many thanks.
Yes, spamhaus is not working anymore if you use a public resolver, using your local resolving DNS server (e.g. the locally installed BIND instance) will still work. That's one option too. That's generally fine, if you use a recent setup with Rspamd, then RBL are not needed anymore. Rspamd and also amavis sue RBL in there weighted results anyway. You can use any email RBL, these are not ispconfig specific. Even multiple RBL's can be inserted into that field.
