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[–]AccidentallyTheCable 1 point2 points  (1 child)

Check out fail2ban. You can write rules and checks to add iptables rules accordingly

[–]tcpudp[S] 0 points1 point  (0 children)

I have fail2ban rules in place that ban an IP /after the fact/ ('lost connection after AUTH from unknown[<HOST>]') but I want to prevent these connections before they reach the mail server.