how get mail when there is any error in web application in asp.net.

i have used the following code and getting the mail when error in application but i also get the mail when the page is running fine. if there is no image found in local server then it also send. The code is given below 

void Application_Error(object sender, EventArgs e) 
    { 
        // Code that runs when an unhandled error occurs
        Exception objError = Server.GetLastError().GetBaseException();
        string error = " <br/><br/>Error in: <b>" + Request.Url.ToString() +
                       " <br/><br/> IP Address:"+ HttpContext.Current.Request.UserHostAddress +
                     " <br/><br/>Error message:" + objError.Message.ToString() +
                     " <br/><b/>Stack Trace: <b/><br/>" + objError.StackTrace.ToString();
 
        SmtpClient smtclient = new SmtpClient();
        MailMessage msg = new MailMessage();
        MailAddress fromAddress = new MailAddress("noreply@abc.com", "www.abc.com");
        msg.From = fromAddress;       
       msg.To.Add("mdikram0530@gmail.com");
        msg.Subject = "Error in the Website";
        msg.Priority = MailPriority.High;
 
        msg.Body = error;
        msg.IsBodyHtml =false;
        smtclient.Host = "mail.abc.com";
        smtclient.Credentials = new System.Net.NetworkCredential("test@abc.com", "123456");
        smtclient.Send(msg);

    }