You need to configure the environment to support the planned changes for email addresses.

References:

https://docs.microsoft.com/en-us/powershell/module/exchange/email-addresses-and-address-books /new-emailaddresspolicy?view=exchange-ps

https:// docs.microsoft.com/en-us/Exchange/email-addresses-and-address-books/email-address-policies/email-address-policies?view=exchserver-2019