Hello, iīm trying to migrate from my production ambient with uses Postfix as SMTP and Cyrus Imap and i need to migrate to my newer server using Zimbra.

I need to migrate in a soft way because we have more than 5.000 accounts and more than 200GB of data, this will need more than 2 days to move using imapsync and i donīt want stop email service in this period.

Like this :
Server A : Postfix and Imap ( And a LDAP )
Server B : Zimbra

I want to put the two servers running in same time, the Server A will be the 'Master' until the Server B be promoted to new master and will turn in Server A.

How i can configure Postfix to send the same messages recieved for Server A a copy to Server B ? ( using the same domain, not a secondary like some example i saw here )

How i can migrate the emails from server A to B in imapsync using a Master account of Postfix ? ( because i donīt want to reset the passwd from the old accounts )

Thanks for the help, i really want to make this migration less painfull possible and i thinks the guys here can help me with this.