Hello!
Given the following configuration within plesk 12.0.18 (centos7):
/etc/postfix/sender_bcc
# contents
a@same.com backup_a@same.com
b@same.com backup_b@same.com
c@same.com backup_c@same.com
/etc/postfix/main.cf
# at the end of the file
sender_bcc_maps = hash:/etc/postfix/sender_bcc
#...