ISPC3, Buster, perfect setup. I have a problem with one of the IP hammering my server every second or less. Code: Sep 5 14:39:13 panda postfix/smtpd: NOQUEUE: reject: RCPT from unknown[188.8.131.52]: 450 4.7.1 <Edco-Edge.edco.local>: Helo command rejected: Host not found; from=<> to=<[email protected]_of_my_client> proto=ESMTP helo=<Edco-Edge.edco.local> I would like to set up Fail2ban to block these attacks. I tried several rules, regxp and so on, but no success (from examples from Google search). Does anybody have suggestion, how to do it properly?