Postfix should send mails to two servers
being in the process of moving my ISPConfig installation to another server (which is going to have the same hostname.domainname, just another IP address), I was wondering if there is a way to create a Postfix transport that
1. sends every mail to the IP address of the new server (which is easy, I guess by putting "* smtp:[<IP address of new server>]" into /etc/postfix/transport)
2. continues to deliver the mail locally, as Postfix always used to.
The two servers are configured identically - with all domainnames, users, configs, etc.
The reason for this question: I hope that this way it wouldn't be an issue how long the DNS transition of the domainnames would take. Mail-wise, the two machines would always be in sync. The user can do an IMAP connect to the old or the new server and will always have the identical inbox.
Could anybody give me a pointer on how to confure a postfix transport that would do exactly this?! Or maybe you have other ideas on how to solve this issue.
Thanks and regards,