SmtpClient Email Not Sent, Not Caught and Not Logged? - asp.net

Question

Our website was meant to send out a particular email, it didnt send the email and it also did not log the error which is unusual as i have a try catch setup which should log the entry in the try or catch section.
1) Why did it not log?
Should i not use Exception and instead use SmtpException and SmptFailedException. If i have this would it have made a difference? If so can you please provide an example.
2) The port we are currently using is 587. As our website is SSL i read we should be using 443 port instead. Would this have made a difference?
The below code is called asynchronously by using
ThreadPool.QueueUserWorkItem(new WaitCallback(SendInstructions), guid);
Which then calls a function that then calls the SendEmail Function below
public static bool SendEmail(String strToAddress, String strFromAddress, String strFromName, String strSubject, String strRecipientName, String strBody, String strEmbeddedImagePath, String strEmbeddedImageName, String strCCReminderEmail)
{
try
{
SmtpClient client = new SmtpClient();
client.EnableSsl = true;
using (MailMessage message = new MailMessage(
new MailAddress(strFromAddress, strFromName),
new MailAddress(strToAddress, strRecipientName)))
{
message.IsBodyHtml = true;
message.Subject = strSubject;
message.Body = strBody;
if (!string.IsNullOrEmpty(strCCReminderEmail))
message.CC.Add(strCCReminderEmail);
client.Send(message);
LogEmail(strFromAddress, strToAddress, strSubject, "Sent", strBody);
return true;
}
}
catch (Exception ex)
{
//log email
LogEmail(strFromAddress, strToAddress, strSubject, "Error", strBody);
throw;
}
}

Answer 1

I had a problem similar when using
ThreadPool.QueueUserWorkItem( new WaitCallback( ...
and then
System.Net.Mail.SmtpClient sC = new System.Net.Mail.SmtpClient(SMTPHost, SMTPPort);
the thread died without throwing an exception.
In my case, the main application thread is exiting before the background threads in the threadpool have had a chance to finish.
The threadpool creates Background worker threads which die as soon as
the main application thread terminates.
so I made a function to sleep 5 seconds and it worked.