Help > Email > Can I prevent people from seeing the other people I sent a message to?
In addition to being able send a
message to several people, known as "Cc" or "carbon copy", you also
have the ability to send a copy to individuals who will be hidden from
the list of recipients. This is known as "Bcc" or "blind carbon copy"
and is typically used when you wish to prevent the initial recipient
from knowing you copied the message to someone else.