IP warming is an extremely important part of beginning to send email via a whitelisted, dedicated IP with any ESP (Email Service Provider). IP Warming is designed to help you establish a positive reputation with ISPs (Internet Service Providers). Every time a new IP address is used to send email, ISPs programmatically monitor email from it in order to verify that it isn’t being used to send spam to users.
https://www.braze.com/academy/Best_Practices/#ip-warming-schedules