I can swear the option was there, but now I can't find it - any clues where it's gone and how to enable it?
Here is what I see now:
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It's a functionality that is enabled at your account level. You need to ask the support to enable it for you.
CC and BCC: When enabled in your account, carbon copy or blind carbon copy recipients to an email send who are not members of the targeted audience. Access is free and you are charged for each CC and BCC email sent.
Reference: Select Audience
For reference anyone searching to enable BCC/CC this is now self-service
Enable one or more of these features in Email Optional Features.
From Name Dropdown of Users
The steps needed:
Now the option is there: