Why can't Hotmail (or other providers) tell the difference between spoof and real emails?

Question

Why can't Hotmail tell the difference between spoof and real emails from a domain (such as blizzard.com)? I get swamped with phishing emails from "blizzard.com" so I put it on my blacklist but then I can't get legitimate emails.

Is there no information in the headers that can be used to definitively determine where the email came from?

Answer 1

• SMTP is designed to allow any host relay messages originally sent by another host. For example, I could run a SMTP server for my own domain, but configure server B to accept mail whenever my server is down and forward it later to its destination.

• Every hop, including the sender (whether legitimate or not), can add any header they wish; for example, a secretary can put the boss' address in From. And so can a spammer. It's not uncommon to see spam with spoofed Received or Date headers too.

• SPF was created to allow a domain's owner to specify which servers are allowed to send messages claiming to be from that domain. blizzard.com has a SPF record, but either Hotmail does not check it at all or ignores the "reject" rule. Or the fake mail is being sent from an allowed host.

• Some mail servers (especially the big ones, such as Gmail or Yahoo! Mail) attach a DKIM digital signature to all outgoing messages. However, while this can prove that a message is legitimate, it does absolutely nothing to detect fake messages, because the recipient just does not know whether DKIM was disabled intentionally or not.

  • When DNSSEC becomes widespread enough, it might be possible to check if the sender has published a DKIM key; however, this would cause other problems.

• There exist ways to digitally sign single messages – PGP and S/MIME – but they, like DKIM, are equally useless against spam.

Answer 2

Problem is that any information which the official Blizzard could put in the headers, the "spoofers" could also put in their headers.