问C# antivirus阻止smtp检查

EN

public static bool Check(string host, string port, string username, string password)
        {
            TcpClient tcpClient = new TcpClient();
            tcpClient.Connect(host, Convert.ToInt32(port));

            NetworkStream netStream = tcpClient.GetStream();
            System.IO.StreamReader strReader = new System.IO.StreamReader(netStream);
            byte[] WriteBuffer = new byte[1024];
            ASCIIEncoding enc = new System.Text.ASCIIEncoding();

            WriteBuffer = enc.GetBytes("USER " + username + "\r\n");
            netStream.Write(WriteBuffer, 0, WriteBuffer.Length);

            WriteBuffer = enc.GetBytes("PASS " + password + "\r\n");
            netStream.Write(WriteBuffer, 0, WriteBuffer.Length);

            if (strReader.ReadLine().Contains("+OK"))
            {
                return true;
            }
            return false;
        }