Case:
- user changes mail address to a domain that is not whitelisted
- user gets mail to confirm that address
- clicking that link results in error There was an error changing your email address. Perhaps the address is already in use?
Apart from the fact that the error message doesn’t help at all, why was the address accepted in the first place?
Although the change is not accepted - hence the whitelisting works - it’s confusing for the user.