Send E-mail notification If a certain value (IP Address) is found in the array

I have a C# console application and want to be able to send an Email to a certain address if any IP addresses that are not local are found in the array, I am assuming I would use a If != statement but i cannot get anything to work. Any tips or help would be greatly appreciated.

    System.Net.IPAddress[] addresslist = Dns.GetHostAddresses(C);
   {
     string IPs = "";
     bool firstIP = true;
     foreach (IPAddress ip in addresslist)
         {
            if (!firstIP)
                {
                   IPs = IPs + ",";

                }
                    IPs = IPs + ip;
                    firstIP = false;
                   }
                     addresslist.ToString();
      if addresslist != { "10.1.20.99"} //example, have multiple IP's
       then //..... this is where I am stuck