I'm not sure how to exactly fix this as I've looked at the Spamhaus PBL fixes, and most seem to be implemented by the ISPConfig installer setup. I am being sent to spam while sending to Gmail addresses and straight out being blocked from outlook's system. I did nothing more configuration wise other than following the Debian Cluster setup and Perfect ubuntu apache server guides. Code: This is the mail system at host miyagi.gethosting.today. I'm sorry to have to inform you that your message could not be delivered to one or more recipients. It's attached below. For further assistance, please send mail to postmaster. If you do so, please include this problem report. You can delete your own text from the attached returned message. The mail system <[email protected]>: host outlook-com.olc.protection.outlook.com[126.96.36.199] said: 550 5.7.1 Client host [188.8.131.52] blocked using Spamhaus. To request removal from this list see http://www.spamhaus.org/lookup.lasso (S3130). [SN1NAM04FT014.eop-NAM04.prod.protection.outlook.com] (in reply to MAIL FROM command) Reporting-MTA: dns; miyagi.gethosting.today X-Postfix-Queue-ID: 0FAC115C04C5 X-Postfix-Sender: rfc822; [email protected] Arrival-Date: Thu, 20 Sep 2018 10:05:53 -0400 (EDT) Final-Recipient: rfc822; [email protected] Original-Recipient: rfc822;[email protected] Action: failed Status: 5.7.1 Remote-MTA: dns; outlook-com.olc.protection.outlook.com Diagnostic-Code: smtp; 550 5.7.1 Client host [184.108.40.206] blocked using Spamhaus. To request removal from this list see http://www.spamhaus.org/lookup.lasso (S3130). [SN1NAM04FT014.eop-NAM04.prod.protection.outlook.com] I tried checking the SMTP Auth settings in postfix, but decided not to touch anything as ISPConfig seems to have done most of the dirty work. So I don't understand why this is happening. When I was running one server it worked fine. Could this be because the cluster setup I did?