By default, the BCC option has been marked as hidden when you compose a new email in Outlook. This step has been taken in order to conserve the space on the screen by hiding options that are no regularly used. If you want to get BCC back, please, follow these steps:
Outlook 2002/2003: Create a new email message, then on the View menu click BCC field. But if it is not there, double click the View menu and it will appear.
Outlook 2007 : Open the new email window, click Options > Fields area > Show BCC.