If it's web based mail (i.e. Gmail, Yahoo mail, etc.) it goes through the web shield.
There is a web based Outlook and there is the "paid" version of Outlook. Only the
paid product is covered by the mail shield, the web based is scanned by the web
shield. Anytime you open an attachment on a web based email the web shield does
the scanning. Once you download and save it to your computer then the file shield kicks in.