I want migrate from Postfix to Zimbra, but I don't want stop the Postfix's services.

I have mydomain.com, the main server is mail.domain.com and has main postfix running. I have a secondary server called zimbra.domain.com and has zimbra server running.

I configured Postfix on mail.domain.com to send all mail recived to zimbra.domain.com using this line:
transport_maps = hash:/etc/postfix/transport

transport file:
@domain.com smtp:zimbra.domain.com

It work but the problem is I want keep or save the mails in mail.domain.com but Postfix move the mails and doesn't keep the mail.

Sorry for my English and ... ¿somebody can help me? Thanks