The example for using EASendMail SMTP component asynchronously demonstrates using AsyncWaitHandle to block execution until the SendMail operation completes, like this:

SmtpClientAsyncResult oResult = oSmtp.BeginSendMail(oServer, oMail, null, null);
while (!oResult.IsCompleted) {
    oResult.AsyncWaitHandle.WaitOne(50, false);
}
oSmtp.EndSendMail(oResult);

Is it possible to use callback delegate? I have tried to use the code like following:

SmtpClientAsyncResult oResult = oSmtp.BeginSendMail(oServer, oMail, 
    new AsyncCallback(AsyncSendCompletedCallback), oSomeStateObject);

//...

private void AsyncSendCompletedCallback(IAsyncResult result)
{
    try
    {
	EASendMail.SmtpClientAsyncResult ar = result as EASendMail.SmtpClientAsyncResult;
        ar.SmtpClientInstance.EndSendMail(ar);
    }
    catch( EASendMail.SmtpTerminatedException )
    {
    }
    catch( Exception ex )
    {
    }
}

This works fine when communication with SMTP completes without problems. If there is a communication error, however, the operation will never complete, i.e. callback procedure seems to newer get called. For example, if wrong password is set, the opeation continues and various events are raised as expected, until the SMTP server responds with status code 535 Bad authentication. Then everything stops, and the callback procedure is never called. This does not happen when AsyncWaitHandle is used.

Can you confirm that callback delegate method is actually supported?

Thanks for the very quick reply.

I have temporarily cirumvented the problem by using BackgroundWorker as follows:

bwWaitAsync = new BackgroundWorker();
bwWaitAsync.DoWork += bwWaitAsync_DoWork;
bwWaitAsync.RunWorkerCompleted += bwWaitAsync_RunWorkerCompleted;

//...

bwWaitAsync.RunWorkerAsync(oSmtp.BeginSendMail(oServer, oMail, null, oSomeStateObject));

//...

void bwWaitAsync_DoWork(object sender, DoWorkEventArgs e)
{
    EASendMail.SmtpClientAsyncResult result = e.Argument as EASendMail.SmtpClientAsyncResult;
    result.AsyncWaitHandle.WaitOne();
    e.Result = result;
}

void bwWaitAsync_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
{
    AsyncSendCompletedCallback(e.Result as EASendMail.SmtpClientAsyncResult);
}

This is not the optimal solution as it creates one more thread, but works fine.

So, there is no rush to fix the bug, I can wait until the next regular release.

Thank you again!

Edited by user Thursday, July 18, 2013 6:31:59 AM(UTC)  | Reason: Not specified

In my development environment, using first a wrong password, and then an unexisting host, EASendMail40.dll worked as expected, errors being reported as exceptions from EndSendMail.

I will be deploying the program at one site tomorrow, and will have it run experimentally during the next week. Will report if any issues arrise.

Thank you, and greetings!