using System;

using System.Linq;

public class Program

{

    public static void Main()

    {

        string ipsFromConfig = "127.128.129.130;43.44.45.46;43.221.58.1;168.192.0.870;";

        string incommingIp = "43.221.58.1";

        string[] ipList = ipsFromConfig.Split(';');

​

        Console.WriteLine((ipList.Contains(incommingIp)) ? "Blacklisted IP" : "IP not in blacklist"); // remove this line

        if (ipList.Contains(incommingIp))

            return;

    }

}