SmtpClients' SendCompleted Event Handler not firing

private void SendMail()
        {

            client = new SmtpClient(mailConfig.Server, mailConfig.Port);

            using (oMessage = new MailMessage() { From = new MailAddress(MailFrom, FromName, Encoding.UTF8) })
            {
                if (MailTo.Count == 1)
                    oMessage.To.Add(new MailAddress(MailTo[0], GDMS.Utilities.Classes.CurrentUser.CurrentUserName));
                else
                {
                    foreach (string s in MailTo)
                        oMessage.To.Add(new MailAddress(s));
                }
                oMessage.Subject = Subject;
                if (CC != null && CC.Count > 0)
                {
                    foreach (string s in CC)
                        oMessage.CC.Add(s);
                }
                if (!String.IsNullOrEmpty(HTMLBody))
                {
                    oMessage.Body = HTMLBody;
                    oMessage.IsBodyHtml = true;
                }
                else
                    if (!String.IsNullOrEmpty(TextBody))
                    {
                        oMessage.Body = TextBody;
                        oMessage.IsBodyHtml = false;
                    }
                if (BCC != null && BCC.Count > 0)
                {
                    foreach (string s in BCC)
                        oMessage.CC.Add(s);
                }
                oMessage.BodyEncoding = Encoding.UTF8;
                oMessage.SubjectEncoding = Encoding.UTF8;
                oMessage.Priority = MailPriority.High;
                client.DeliveryMethod = SmtpDeliveryMethod.Network;
                client.UseDefaultCredentials = false;
                client.Credentials = new NetworkCredential(mailConfig.Username, mailConfig.Password);
                if (mailConfig.Server.ToUpper().Contains("GMAIL"))
                    client.EnableSsl = true;
                client.SendCompleted += new SendCompletedEventHandler(MailSendingComplete);
                //client.Send(oMessage);
                try
                {
                    client.SendAsync(oMessage, "Sending Mail");
                }
                catch (Exception ex) { string msg = ex.Message; }
                finally
                {
                    mailSent = true;
                }
            }

        }

        private void MailSendingComplete(object sender, AsyncCompletedEventArgs e)
        {
            String token = (string)e.UserState;
            if (e.Cancelled)
            {
                if (SendMailCompleted != null)
                {
                    SendMailCompleted(this, string.Format("[{0}] Send canceled.", token));
                }
            }
            if (e.Error != null)
            {
                if (SendMailCompleted != null)
                {
                    SendMailCompleted(this, string.Format("[{0}] {1}", token, e.Error.Message));
                }
            }
            else
            {
                if (SendMailCompleted != null)
                {
                    SendMailCompleted(this, "Message sent.");
                }
            }
            mailSent = true;
        }