Mailbox name not allowed. The server response was: sorry, Authentication failed or timed out. Please do get messages first to authenticate yourself.(#4.4.3)

See more:

C#

ASP.NET

I am getting an error "Mailbox name not allowed. The server response was: sorry, Authentication failed or timed out. Please do get messages first to authenticate yourself.(#4.4.3)" while sending Message. I am using Rediffmailpro so according to that i had changed the port address . but when i am setting gmail settings its working fine . please help to solve the problem .

string from = "noreply@mail.org";
       string to = "mail1@name.org";
       string Password = "password$";
       int port = Convert.ToInt32(ConfigurationManager.AppSettings["port"]);
       string smtp = Convert.ToString(ConfigurationManager.AppSettings["smtp"]);
       string Subject = "Enquiry";
       string body = "Sender Name :" + txtname.Text + "\n" +
                    "Phone :" + txtphone.Text + "\n" +
                    "Email :" + txtemail.Text + "\n" +
                    "Address :" + txtaddress.Text + "\n"
                    + "Enquiry :" + txtenquiry.Text;
       MailMessage Msg = new MailMessage(from, to, Subject, body);
       //Smtp Host is the  name or Ip host of the computer used for sending mail
       SmtpClient smtpobj = new SmtpClient("smtp.rediffmailpro.com", 25);
       smtpobj.Host = "smtp.rediffmailpro.com";
       smtpobj.Port = 25;
       smtpobj.EnableSsl =false;
       smtpobj.UseDefaultCredentials = true;
       smtpobj.Credentials = new System.Net.NetworkCredential(from, Password);

       try
       {
           smtpobj.Send(Msg);
           ScriptManager.RegisterStartupScript(this.Page, this.GetType(), "Hi", "<script type='text/javascript'>alert('Your Message Has Been Send ');</script>", false);
           CleaContents();
       }
       catch (Exception ex)
       {
           lbltext.Text = ex.Message;
       }