[jlgaddis]

Not exactly. Some methods won't be nearly as effective (such as filtering on the message body) but others (such as SPF, DKIM, and RBLs) will still work just as well as they do today.

Now that I think about, just the encryption itself will increase the computational cost of sending out spam e-mails. While today a spammer can blast out an e-mail to 100 recipients very quickly, it'll take a fair bit longer to do once the spammer has to query and retrieve 100 public keys (one for each of the recipients) and then encrypt the e-mail 100 times over.

[rocqua]

A large part of spam detection remains machine learning on message bodies. Something this would make impossible.

As for encrypting the e-mail 100 times. AES acceleration is great in CPU's, and you can cache public keys. The only real-ish bottleneck could be key-generation.

That said, someone else had a decent idea. Require white-listing for encrypted e-mail.