ACT! has been specifically designed to not automatically attach emails to ACT! contacts as they are received. Instead, two add-ins have been added to Outlook to do this - the Attach to ACT! Contacts, and Quick Attach shortcuts. Of course, ACT! can be (and is usually) configured to have emails automatically attach to contacts as they are sent.
However, if you prefer to have emails automatically attach as they enter your Outlook Inbox, this can be achieved by creating an Outlook Rule. To find out how, please read more.