Use BBC instead of To: or CCC: that way no one will see anybody elses

Put your own email address in the ‘To’ field, and put all your recipients’ addresses in the BCC field. This way they will see only your address, which is okay because YOU are the sender. But no one else will see any of the other addresses.

use the BCC option. normally all mails require at least one addressee to be in the To field. rest can be in the BCC (Blind Carbon copy) they will not know who are the other recipients of the mail