One problem in this are bad actors. German Telecom for example (t-online.de) only accepts mails from servers it whitelists. To get whitelisted you have to appl

One problem in this are bad actors. German Telecom for example (t-online.de) only accepts mails from servers it whitelists. To get whitelisted you have to apply with them and your domain HAS to have a website with an Impressum, your clear legal name AND an email that is NOT your domain for emergency contact. It is insane. If every provider would act like that, email would die in a month.