Enabling BCC in Outlook

Outlook 2010, Outlook 2013 and Outlook 2016

When composing a message, select the Options tab and press the “Show BCC” and “Show From” buttons to enable them.

Using Outlook 2013 or Outlook 2016 and reply or forward an email from the Reading Pane, the Show Fields group can be found all the way to the right on the Message tab.
Note 1: The From field will always be visible in Outlook 2010, Outlook 2013 and Outlook 2016 when you have more than one account configured. You cannot disable the From field then either.

Outlook 2007

Select the Options tab and press the “Show BCC” and “Show From” buttons to enable them.

Outlook 2003 and previous with Outlook as the email editor

View-> BCC Field
View-> From Field