Failure during email send through rediffmail smtp client

See more:

C#

SmtpClient

Hi,
Here i am facing problem during email send via rediffmail smtp client. Here email send properly using gmail and webmail(smtp.logix.in)

Following is my code.....

MailMessage Message = new MailMessage();
Message.IsBodyHtml = true;
string to=txtCustEmail.Text;
string from = txtYourEmail.Text;
string password = txtPass.Text;


Message.To.Add(new MailAddress(to));
Message.From = (new MailAddress(from, "ADMIN"));
Message.Subject = txtMsgSub.Text;
Message.Body = txtMsgBody.Text;
Message.Attachments.Add(new Attachment("D:\\Excise2.xlsx"));


NetworkCredential NetworkCred = new NetworkCredential(from, password);

SmtpClient sc =new SmtpClient();
if (radioButton1.Checked==true)
{
   sc = new SmtpClient("smtp.gmail.com");
}
if (radioButton2.Checked==true)
{
     sc = new SmtpClient("smtp.logix.in");
}
if (radioButton3.Checked == true)
{
    sc = new SmtpClient("smtp.rediffmail.com");
}
sc.Port = 587;

//sc.Host=
sc.Credentials = NetworkCred;
sc.EnableSsl = true;

sc.Send(Message);
MessageBox.Show("Email send to " + Message.To);

Message.Dispose();

Email send Properly through gmail and logix but not for rediffmail.com even my rediffmail credential are correct.It shows following exception

SmtpException was handled...Failure sending mail.


Please help me........
Thanks