@kinnison@hisham_hm#DKIM does help against spoofing headers such as "From:", and the mail body. It comes with the major caveat (amongst others) that once leaked, you have no way* to plausibly deny authorship of emails. IIRC this has happened with Hillary Clinton's mails on Wikileaks.
*you can regularly rotate your signing keys and publish the old keys, however there does not seem to be a standard way of doing this.