You can view the BCC field when you are writing an email by tapping on the "..." button in the top of the new email screen.

You can set the "Default BCC" in the "Email" section of the App Settings. View
This will include this email address in the BCC field for all sent emails.

You can also set a "Default BCC" for each email account in the "Appearance" section of the edit email account screen. View