Email in Twilio Flex is not a HIPAA Eligible Service and should not be used in workflows that are subject to HIPAA.
Warming up your IP allows you to gradually send more emails over your new IP to establish a good sender reputation.
Note that only one IP address is supported for Email in Flex.
When you add a new dedicated IP address to your account, you need to warm it up. You also need to warm up your IP address if you haven't sent any email from it in more than 30 days.
It is much easier to establish a positive reputation as a new sender than it is to repair an existing reputation.
You can use SendGrid's automated IP warmup feature to manage this process automatically. Or, if you prefer, you can manually control the warmup schedule by gradually sending more and more email over your IP address following SendGrid's recommended IP warmup schedule.
For more information about both of these options, see Warming Up an IP Address.