Sending Email using Windows Application C#

Question

I am developing a application to send Email from windows application using c#. I have written the following code.

try

{

btnSend.Enabled = false;

btnCancel.Visible = true;

MailMessage message = new MailMessage();

SmtpClient smtp = new SmtpClient("smtp.gmail.com");

message.From = new MailAddress(txtFrom.Text);

message.To.Add(txtTo.Text);

message.CC.Add(txtCC.Text);

message.Subject = txtSubject.Text;

message.Body = txtMessage.Text;

if (txtAttachment.Text.Length > 0)

{

if (System.IO.File.Exists(txtAttachment.Text))

{

Attachment attach = new Attachment(txtAttachment.Text);

message.Attachments.Add(attach);

}

}

smtp.Port = 465;

smtp.Credentials = new NetworkCredential(txtFrom.Text, txtPasskey.Text);

smtp.EnableSsl = true;

smtp.DeliveryMethod = SmtpDeliveryMethod.Network;

smtp.Send(message);

MessageBox.Show("Mail Sent.", "Email");

}

catch (Exception ex)

{

MessageBox.Show(ex.Message);

btnCancel.Visible = false;

btnSend.Enabled = true;

}

 

Now the problem here is :-

If I use port 465 then it gives exception as Failure sending mail.

If I use port 25 or 587 then it gives exception as The SMTP server requires a secure connection or the client was not authenticated. The server response was 5.5.1 Authentication required. Learn more at.

 

Note:- I used my gmail ID as sender, (I have two steps verification enabled on my gmail account) 

 

How can I solve this??