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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?

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up vote 5 down vote accepted

Take a look at SPF, it's pretty much what you're describing.

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Very nice. I knew this wasn't something I could come up with first :) Are there any known implementations of SPF? And why isn't the whole world using this already? –  jao Jul 12 '12 at 19:07
    
@jao It's pretty widely deployed and used as part of spam scoring by most major mail providers, but since it's optional and must be implemented by the sender, it's still not ubiquitous. –  Shane Madden Jul 13 '12 at 3:49
    
Thanks. I'm going to implement this where I can. –  jao Jul 13 '12 at 6:35
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