Leads- sending email in CC, shoul be better in BCC

I have Leads, and trying to send (as test)some 10 email to the Leads Email addresses.
by clicking the left square for filling in.

I see that all these TEN are in the CC, so presume readable to everybody of the 10 contacts.??
Can I change it to BCC, that seems to be more better…?! and not visible to the others
I have win10, and local Bitnami SuiteCRM 7.6.4 (which is for me the best option)

Thanks for help.