Allow automatic BCCing of outgoing email?
When this option is set to Yes, you will be able to configure each
virtual server so that email sent by it's mail users is BCCd to a separate
address. However, this will only work when the Postfix mail server is being
used and if the sender_bcc_maps directive is set in its
main.cf file.
If Postfix also has the recipient_bcc_maps directive set, you will
also have the option to set an address for BCCing incoming messages.