SpIDer Mail scans email messages only if you are using a local mail client (for example, MS Outlook, Mozilla Thunderbird, etc.). Moreover, emails are scanned as they are downloaded. When the list of new messages is displayed on the server, they may not yet have been physically downloaded by you, and, thus, at that moment, they are still unscanned.
If an email is opened via a browser, it is not downloaded to the local computer. Instead, it is rendered by the browser according to the message located on the remote server. It is impossible to scan an email if it is not fully downloaded. But any attachments you save from an email message on the disk of your computer will be scanned by SpIDer Guard.
