Have you restarted the Mail Shield or rebooted to see if that will apply the changes to your settings ?
That said if you are using MS Outlook, that has its own avast plugin/add-in:
Is it using that, ensure that it isn't disabled. Sorry I can't be of more help as I don't use MS Outlook.
That said 2 if you are using Web Mail via your browser, I don't know if the Mail Shield settings