"In addition, in some potential realizations of IM2000, email would become mutable in practice" That objection is invalid, as common and widespread DKIM messag

"In addition, in some potential realizations of IM2000, email would become mutable in practice" That objection is invalid, as common and widespread DKIM message signature can be pushed with other headers. Author is likely aware of this, so he inserted a qualifier "in some potential realizations". Then it follows that this is not objection to IM2000, but to an easily fixed realization flaw. This makes the author look like he has an agenda.