Public Function SendMailMessage(Optional ByVal m_msg_FromAddress As String = vbNullString,
...
                                  Optional ByVal m_CallbackFunction As SendCompletedEventHandler = Nothing,
                                  Optional ByVal m_emailToken As String = vbNullString,
                                  Optional ByRef str_error As String = vbNullString
                                  ) As Boolean

          If IsNothing(m_CallbackFunction) Then
            AddLogCDO(Now.ToString & Chr(9) & "Sending mail")
            .Send(message)
            AddLogCDO(Now.ToString & Chr(9) & "Sending mail...Done")
            AddLogCDO("-------------------------")
            Return True
          Else
            AddLogCDO(Now.ToString & Chr(9) & "Sending mail asynchronously")
            AddLogCDO(Chr(9) & Chr(9) & "Token=" & m_emailToken)
            AddHandler client.SendCompleted, m_CallbackFunction
            .SendAsync(message, m_emailToken)
            AddLogCDO(Now.ToString & Chr(9) & "Sending mail asynchronously...waiting for the result")
            AddLogCDO("-------------------------")
            Return True
          End If
...
    If SendMailMessage("sender@hotmail.com",...
     ..."smtp.live.com", 587, True, "sender@hotmail.com", "password", True, False, AddressOf SendCompletedCallback, "RandomToken", str_err) ...

  Private Sub SendCompletedCallback(ByVal sender As Object, ByVal e As AsyncCompletedEventArgs)
    ' Get the unique identifier for this asynchronous operation. 
    Dim token As String = CStr(e.UserState)

    AddLogCDO("-------------------------")
    If e.Error IsNot Nothing Then
      Dim str_err As String = "Error code: " & e.Error.HResult.ToString & " (" & e.Error.Message & ")"
      AddLogCDO(Now.ToString & Chr(9) & "Sending mail asynchronously...Failed. " & str_err)
      AddLogCDO(Chr(9) & Chr(9) & "Token=" & token)
      AddLogCDO("-------------------------")
      MsgBox("Sending mail...Failed." & vbCrLf & str_err, _
       vbCritical + vbOKOnly, "Sending mail failed.")
    Else
      AddLogCDO(Now.ToString & Chr(9) & "Sending mail asynchronously...Done")
      AddLogCDO(Chr(9) & Chr(9) & "Token=" & token)
      AddLogCDO("-------------------------")
      MsgBox("Test mail was sent successfully!", vbInformation + vbOKOnly, "Email was sent")
    End If

  End Sub