In your place, I would start by checking the following points:
• Where are the MX pointing? The result of the MX probably goes to your Firewall “so check the proxy, NAT etc. »
• If it's to the Production server, it's good, otherwise the streams will have to be changed.
• Check the sending connectors "check / add the production server"
• Check the reception connectors "especially if you have a relay, you will have to redo the same configuration on the production side"
• Check if you are not using a public folder “if so, they will have to be migrated”
Once you have checked the following points you can turn off the server temporarily, the time to validate the proper functioning of the production server.
After that You will just have to turn on the server and uninstall exchange