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Hi, Iam preparing a small interview email project in with c#. But the same project works well in Windows Forms.
But when I try to send from WebForms its' giving error like

" The SMTP server requires a secure connection or the client has not authenticated. The server response was 5.5.1 authentication required"

My Codes :-

    System.Net.Mail.MailMessage Mail = new System.Net.Mail.MailMessage();
    System.Net.Mail.SmtpClient SmtpServer = new System.Net.Mail.SmtpClient("");
    Mail.From = new System.Net.Mail.MailAddress("");
    Mail.To.Add(new System.Net.Mail.MailAddress(this.DropDownList1.SelectedItem.Text));
    if (TextBox1.Text.Trim().Length > 0)
    if (TextBox2.Text.Trim().Length > 0)
    Mail.Subject = this.TextBox3.Text;
    if (MyInput1.PostedFile.FileName.Trim().Length>0)
        System.Net.Mail.Attachment My_Attach = new System.Net.Mail.Attachment(MyInput1.PostedFile.FileName);
string MyImgString64 = "/9j/4AAQSkZJRgABAQEAYABgAAD/2wBD....";
Byte[] bitmapData = Convert.FromBase64String(FixBase64ForImage(MyImgString64));
System.IO.MemoryStream streamBitmap = new System.IO.MemoryStream(bitmapData);

System.Net.Mail.LinkedResource imageToInline = new System.Net.Mail.LinkedResource(streamBitmap, System.Net.Mime.MediaTypeNames.Image.Jpeg);
imageToInline.ContentId = "MyImage";
System.Net.Mail.AlternateView av1 = System.Net.Mail.AlternateView.CreateAlternateViewFromString("<html><body><img src=cid:MyImage/><br></body></html>" + TextBox4.Text, null, System.Net.Mime.MediaTypeNames.Text.Html);
Mail.IsBodyHtml = true;

Mail.BodyEncoding = System.Text.Encoding.UTF8;
SmtpServer.Port = 587;
SmtpServer.Credentials = new System.Net.NetworkCredential("", "123456");
SmtpServer.EnableSsl = true;
MessageBox.Show(this, "Sending Mail Status -> Success....!!!");
catch (Exception ex) {
   MessageBox.Show(this, ex.Message);  

Thanks Again

What I have tried:

Sending emails from web forms
Updated 11-Aug-17 2:04am
F-ES Sitecore 11-Aug-17 4:15am    
This question is asked every day, please do basic research like using google before you ask a question, this is thoroughly documented.

1 solution

I am preparing a small interview email project

If this is a job interview assessment, then the only advice that I can give you is that others have experienced the same problem. Use Google Search and you will find helpful information on there. I always start with the error message: the SMTP server requires a secure connection or the client has not authenticate - Google Search[^]
Share this answer
Paramu1973 11-Aug-17 2:26am    
Graeme Iam doing google search for past 2 days. I can't get and then I post here to get advice. Thanks for your advice.
Graeme_Grant 11-Aug-17 2:32am    
Please re-read what I have posted. There is a Google Search link in there with what looks like answers to me.

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