The SMTP server requires a secure connection, or the client failed authentication. Server response: 5.5.1 Authentication required.

Question

Possible duplicate:
The SMTP server requires a secure connection, or the client failed authentication. Server response: 5.5.1 Authentication required

I had a problem when I run this code, then an error occurred: "The SMTP server requires a secure connection or the client did not authenticate. Server response: 5.5.1 Authentication is required."

And my code is:

the code

protected void ImageButton1_Click(object sender, ImageClickEventArgs e) { MailMessage mail = new MailMessage(); mail.To.Add(" [e-mail] "); mail.From = new MailAddress(" [e-mail] "); 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(" [e-mail] ", "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 do you host your site? Gmail prevents unrecognized access to your accounts. Try this code and then go to you in gmail and it will ask you if there was an attempt to access you. Allow the application and you're done.