Yesterday I was upgrade my mail server (zimbra 6.0.1 to 6.0.3 version).
When I use 6.0.1, I manually modified postfix configuration file "main.cf" to realise function of reserve copying of all mail on a separate box (sender_bcc_maps and recipient_bcc_maps).
After upgrade to 6.0.3, zimbra installator was replace config file main.cf to default and remove files: recipient_maps_bcc.db, sender_maps_bcc.db. Thus mail backup function was disabled. Later, I manually restore this files from my old zimbra backup and now reserve mail copying works well on Zimbra 6.0.3.
It is possible, that the future versions of installators will not replace modified user configuration files to default?