Spam is a huge problem these days, especially spam sent with your e-mail address as the sender. I think I have a simple solution but I'd like to hear from you what is wrong with it or why it is infeasible.
My idea is that a recipient server checks if the IP mentioned in the sender is the registered, or authorized, SMTP sender for that domain.
For example: all mail from @example.com has to be send through mail.example.com. If it is send through mailer.spammer.ru for instance than the recipient should block the mail.
A way to list authorized SMTP servers is in a DNS TXT record.
So is this achievable? Or does something like this already exist?