Any time you move email services to a new network with a new IP address, you need check out the IP’s reputation before switching over, just in case it used to be run by a spammer.
ISC Diary | Is “Reputation Backscatter” a Thing?
I recently migrated a client from a 10mbps internet uplink to a new 100mbps uplink with a wireless 10mbps backup. As part of this, they of course got new IP addresses.