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.