How to migrate step by step between mail servers?

Question

Mail server

Good day.
There are two mail servers, and I need to migrate the mail domain (domain1) along with mailboxes and content from the first to the second.
New Centos 7 server : iredmail -0.9.6, iRedAdmin-Pro-2.6.0/ Postfix /Dovecot/MariaDB-Server/Nginx.
Two mail domains (domain2 and domain3) are already spinning on the new server.
As soon as I create on it the domain that needs to be transferred, mail exchange between servers becomes impossible, because. the new server tries to process letters from domain1 as its internal ones, which it naturally cannot do. Messages are not delivered even if domain1 is in the off state on the new server. Moreover, the server itself determines the IP address of the domain1 DNS record correctly.
Given the number of boxes and their total volume, it will not be possible to transfer them all at once with time restrictions on delivery. Therefore, I would like to break en parts.
Is it possible to make iredmail (or rather Postfix ) ignore the presence of domain1 on it and accept/send mail from that domain on another server?

Answer 1

well, I would suggest that you
first sync mailboxes (old -> new), you can use rsync
then on the new postfix settings for domain1, change the address on the dns server
final rsync (old -> new) in case something managed to come to the old one
this is if you can’t stop postfix on the old one