I am new to manage exchange and I am facing an issue.
I have 2 exchange 2016 instances running.
At the moment I am migrating all the mailboxes from server one to server 2.
The server 2 is the one that will be the primary and the first one will be decommissioned.
The MX record on the DNS is pointing to the second server.
The DNS also contains a PTR record for the second server ip address to resolve into mail.domain.com.
Some mailbox is on server one and some on server 2 (because I am migrating them)
The server one doesn't have a PTR record on it.
What's happening is that some email is bounced back because the target mail server doesn't find a PTR record for server 1.
I don't understand why as the facing exchange server is the server number 2.
In the DNS there is nothing pointing to server 1.
Why some email are still sent using the server number 1?