Email Gateway sends email more than once

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ASP.NET

I m working on the email gateway. Different applications provide me email recipient and email content and i send email to those recipients. My application requires that i should try sending mails upto 6 times if mail sending fails for first time.

To track this i have used asynchrounous method to send emails and MailDeliveryComplete event handler . So that i could know that whether emails are sent or not. The MailDeliveryComplete event handler returns false if error occurs in sending mail else returns true.

So if it returns false i try to send email again and this i do for max 6 times.
But my problem is although the event handler returns false, sometimes it actually sends mail and since it has returned me false earlier i tried sending it again and hence the mail is delivered to recipient twice.

Can someone help me to handle this? Please tell me how can i decide whether mail is sent successfully. I searched on the Internet, it gave me option of asynchrounous method to sending emails, which had above issue.

My code is

SmtpClientObj.SendCompleted += new SendCompletedEventHandler(MailDeliveryComplete);

// SmtpClientObj.Send(Mail);
SmtpClientObj.SendAsync(Mail, "Message");

static void MailDeliveryComplete(object sender,
System.ComponentModel.AsyncCompletedEventArgs e)
    {
        //Console.WriteLine("Message \"{0}\".", e.UserState);

        if (e.Error != null)
        {
            //Console.WriteLine("Error sending email.");
            mailSent = false;
        }
        else if (e.Cancelled)
        {
            // Console.WriteLine("Sending of email cancelled.");
            mailSent = false;
        }
        else
        {
            //Console.WriteLine("Message sent.");
            mailSent = true;
        }
    }

Here mailSent is a global variable set to default value false and i m calling Asynchrounous method of smtp object to send mail which invokes MailDeliveryComplete event on async call and returns true or false.