Mail from old server goes to old server, not to new!

I have 2 servers: Old one Debian6 and new one Debian9, both have virtualmin.
Old server have 2 domains and
I moved to new server and disabled it on old server (not removed). Made changes on hosting provider.
Now when I send e-mail to from gmail or yahoo or other it coming to new server as need. But if send e-mail to from old server domain to it still coming to old server.

Where and what I need to configure to let old server know he must send to new server???

Thank you in advance!