The SMTP server requires a secure connection or the client was not authenticated. The server response was: 5.5.1 Authentication Required. [duplicate]

Question

Possible Duplicate:
The SMTP server requires a secure connection or the client was not authenticated. The server response was: 5.5.1 Authentication Required

I have a problem when i m run this code then error is occured that "The SMTP server requires a secure connection or the client was not authenticated. The server response was: 5.5.1 Authentication Required. "

And my code is:

Code

protected void ImageButton1_Click(object sender, ImageClickEventArgs e)
{

    MailMessage mail = new MailMessage();
    mail.To.Add("[email protected]");
    mail.From = new MailAddress("[email protected]");
    string body = "<table><tr><td>Company Name:</td><td>" + txt_cname.Text + "</td></tr><tr><td>Address With No.:</td><td>" + txt_addwithno.Text + "</td></tr><tr><td>Contact Person:</td><td>" + txt_conperson.Text + "</td></tr><tr><td>Email Id</td><td>" + txt_email.Text + "</td></tr><tr><td>Description</td><td>" + txt_description.Text + "</td></tr></table>";
    mail.Body = body;
    mail.IsBodyHtml = true;
    SmtpClient smtp = new SmtpClient();
    smtp.Host = "smtp.gmail.com";
    smtp.Port = 587;

    smtp.Credentials = new System.Net.NetworkCredential("[email protected]", "12345");
    smtp.EnableSsl = true;
    smtp.Send(mail);


    txt_cname.Focus();
    txt_cname.Text = "";
    txt_addwithno.Text = "";
    txt_conperson.Text = "";
    txt_email.Text = "";
    txt_description.Text = "";

}

Answer 1

Where are you hosting your website? Gmail prevents unrecognized access to your accounts. Try to execute this code and then go to you gmail and it will ask you if the access try was from you. Allow the application and you are done.