Can I change the chosen email address of a user?
You can change the email address of a user by creating the required email address as email alias. Once the alias is created, you can make this as the default email address for the user.
Log into mailadmin.zoho.com as the Admin
Click User details and select the user
Select Mail accounts > Add new alias
Create the required email address as alias
Click Save
To change the alias as Mailbox address:
Click the link Change next to mailbox address
Choose the new domain based email address from the drop down
Click Save to change the new email address as Mailbox address.
Refer
here for detailed instructions.
You can optionally remove the older email address associated with the account, if you no longer need it.
Note: Only organization users will be able to change the email address. This is not applicable to personal account users.