Concerns about “Author” Based MTA Registration Administrative challenges for many usage scenarios Imagine equivalent restrictions for postal mail or telephony Does not work for mobile laptop, kiosks, other 3rd-parties Not really “authentication” and not really useful beyond Spam And deployment is expensive Some proposals redefine email semantics Mail-From, … Sender re-writing Limits ability to do real store-and-forward Last MTA before receiver analysis must be Mail-From registered “Policy” publishing service Receivers cannot give highly differential handling in large scale |