To see if avast! is scanning emails, check one of these points:
1) Is the avast icon (the special one of email scanning) be shown in the system tray?
2) Is your email header with the lines
X-Antivirus: avast! (VPS XXXXXX-X, XX/XX/2009), Inbound message and
X-Antivirus-Status: Clean? (Right click the message, choose Properties and Details)
3) Are clean notes added at the bottom of the email? (Internet Mail provider settings)
You can test the security of your email system here: http://www.gfi.com/emailsecuritytest/To see the Standard Shield and other protection:
1) Right click the icon once and see what are the 'last scanned files'...
2) Use eicar virus test.
Do you have any other antivirus in this computer? Had in the past?