SmtpClient.SendAsync bug in ASP.NET 2.0 - asynchronous

Question

I may be wrong, but if you are working with SmtpClient.SendAsync in ASP.NET
2.0 and it throws an exception, the thread processing the request waits
indefinitely for the operation to complete.
To reproduce this problem, simply use an invalid SMTP address for the host
that could not be resolved when sending an email.
Note that you should set Page.Async = true to use SendAsync.
If Page.Async is set to false and Send throws an exception the thread
does not block, and the page is processed correctly.
TIA.

Answer 1

Note that you should set Page.Async = true to use SendAsync.
Please explain the rationale behind this. Misunderstanding what Page.Async does may be the cause of your problems.
Sorry, I was unable to get an example working that reproduced the problem.
See http://msdn.microsoft.com/en-us/magazine/cc163725.aspx (WICKED CODE: Asynchronous Pages in ASP.NET 2.0)
EDIT: Looking at your code example, I can see that you're not using RegisterAsyncTask() and the PageAsyncTask class. I think you must do this when executing asynchronous tasks on a Page where #Async is set to true. The example from MSDN Magazine looks like this:
protected void Page_Load(object sender, EventArgs e)
{
PageAsyncTask task = new PageAsyncTask(
new BeginEventHandler(BeginAsyncOperation),
new EndEventHandler(EndAsyncOperation),
new EndEventHandler(TimeoutAsyncOperation),
null
);
RegisterAsyncTask(task);
}
Inside BeginAsyncOperation, then, should you send a mail asynchronously.

Answer 2

RegisterAsyncTask could not be used.
Look at the BeginEventHandler delegate:
public delegate IAsyncResult BeginEventHandler(
Object sender,
EventArgs e,
AsyncCallback cb,
Object extraData
)
It should return an IAsyncResult.
Now look at the SmtpClient.SendAsync function :
public void SendAsync(
MailMessage message,
Object userToken
)
There is no return value.
Anyway this is working fine, as long as SmtpClient.SendAsync does not throw an exception.

Answer 3

Here is mine. Give it a try.
public partial class _Default : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{
// Using an incorrect SMTP server
SmtpClient client = new SmtpClient(#"smtp.nowhere.private");
// Specify the e-mail sender.
// Create a mailing address that includes a UTF8 character
// in the display name.
MailAddress from = new MailAddress("someone#somewhere.com",
"SOMEONE" + (char)0xD8 + " SOMEWHERE",
System.Text.Encoding.UTF8);
// Set destinations for the e-mail message.
MailAddress to = new MailAddress("someone#somewhere.com");
// Specify the message content.
MailMessage message = new MailMessage(from, to);
message.Body = "This is a test e-mail message sent by an application. ";
// Include some non-ASCII characters in body and subject.
string someArrows = new string(new char[] { '\u2190', '\u2191', '\u2192', '\u2193' });
message.Body += Environment.NewLine + someArrows;
message.BodyEncoding = System.Text.Encoding.UTF8;
message.Subject = "test message 1" + someArrows;
message.SubjectEncoding = System.Text.Encoding.UTF8;
// Set the method that is called back when the send operation ends.
client.SendCompleted += new
SendCompletedEventHandler(SendCompletedCallback);
// The userState can be any object that allows your callback
// method to identify this send operation.
// For this example, the userToken is a string constant.
string userState = "test message1";
try
{
client.SendAsync(message, userState);
}
catch (System.Net.Mail.SmtpException ex)
{
Response.Write(string.Format("Send Error [{0}].", ex.InnerException.Message));
}
finally
{
}
}
private void SendCompletedCallback(object sender, AsyncCompletedEventArgs e)
{
// Get the unique identifier for this asynchronous operation.
String token = (string)e.UserState;
if (e.Cancelled)
{
Response.Write(string.Format("[{0}] Send canceled.", token));
}
if (e.Error != null)
{
Response.Write(string.Format("[{0}] {1}", token, e.Error.ToString()));
}
else
{
Response.Write("Message sent.");
}
}
}