If I am understanding your question, NAV and AVAST will catch the virus
before it is made available to the user for viewing or saving. I thought
AVG had a mail scanning option for Outlook. I don't think it matters
much, the virus will be detected when you go to open or save it. As far
as I can see you just save a little time. It may also depend on your
mail client, I'm not sure if some may leave the attachment on the server
until requested. I use mailwasher which of course does just that. For
short messages that I don't need to save I don't even bother with the
mail client.
Dave Cohen