One common frustration regarding Apple design are the choices they make for default tasks in their software. Many times they change the default configurations in software upgrades.
You might ask, what the heck happened to Bcc? In the default configuration, Apple currently has the Bcc field configuration turned off, and only the cc field configuration turned on.
To turn Bcc on, you can simultaneously type/press the Command-Option-B keys.
You can also go the VIEW menu and look for the option to check the Bcc Address Field. It will stay on in subsequent emails, unless you deselect it from the menu or press Command-Option-B again.
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cc means carbon copy, and bcc means blind carbon copy. The terms originate from old-fashioned paper letter when carbon paper was used to type a second letter underneath the original letter in a typewriter.