we need all sent emails from some clients need to be cc to a backup account
some example could be :
For better control over this process, use sender_bcc_maps and recipient_bcc_maps; some judicious use of regex maps allows you to copy the messages to the same user on an archive domain - for both senders and recipients, like so:
sender_bcc_maps = regexp:/etc/postfix/archive_domain recipient_bcc_maps = regexp:/etc/postfix/archive_domain
In /etc/postfix/archive_domain:
/^([^@]+)@example.com$/ $1@archive.example.com
You can now handle mail to @archive.example.com however you please.