Sending mass email in ASP.NET - asp.net

Question

This is my code to send lots of emails. I want to optimize this code to be sure that it will work and can successfully send all emails. What should I do? I know that putting interrupts between sending might be useful but how can I do this?
The main problem is avoiding classify emails as spam and decreasing number of failed sent emails.
var list = from c in context.Emails orderby c.EmailAddress select c.EmailAddress;
MailMessage mail = new MailMessage();
try
{
mail.From = new MailAddress(txtfrom.Text);
foreach (var c in list)
{
mail.To.Add(new MailAddress(c.ToString()));
}
mail.Subject = txtSub.Text;
mail.IsBodyHtml = true;
mail.Body = txtBody.Text;
if (FileUpload1.HasFile)
{
mail.Attachments.Add(new Attachment(
FileUpload1.PostedFile.InputStream, FileUpload1.FileName));
}
SmtpClient smtp = new SmtpClient();
smtp.Send(mail);
}
catch (Exception)
{
//exception handling
}

Answer 1

I would advise you against adding all reciepients into the same mail message.
Rather use this code:
mail.From = new MailAddress(txtfrom.Text);
mail.Subject = txtSub.Text;
mail.IsBodyHtml = true;
mail.Body = txtBody.Text;
if (FileUpload1.HasFile)
{
mail.Attachments.Add(new Attachment(FileUpload1.PostedFile.InputStream, FileUpload1.FileName));
}
SmtpClient smtp = new SmtpClient();
foreach (var c in list)
{
mail.To.Clear();
mail.To.Add(new MailAddress(c.ToString()));
smtp.Send(mail);
}

Answer 2

With a little due diligence, this can be accomplished with a very simple console application which can be called from the Web form to dispatch the emails. By diligence, I mean to insert a pause between batches so that the mail server won't get bogged down. For example, if you were grabbing the addresses from a DB and sending them out, you could have something like:
if ((count >= 100) && (count % 100 == 0))
Thread.Sleep(30000);
-----------------------------------------
// Web form code-behind
// Pass subject and message strings as params to console app
ProcessStartInfo info = new ProcessStartInfo();
string arguments = String.Format(#"""{0}"" ""{1}""",
subjectText.Text.Replace(#"""", #""""""),
messageText.Text.Replace(#"""", #""""""));
info.FileName = MAILER_FILEPATH;
Process process = Process.Start(info.FileName, arguments);
Process.Start(info);
More info here: Calling Console Application from Web Form