Spammers Most Likely Users Of E-Mail Authentication (TechWeb) [LWN.net]

Spammers Most Likely Users Of E-Mail Authentication (TechWeb)

Posted Jul 13, 2005 17:10 UTC (Wed) by TwoTimeGrime (guest, #11688)
In reply to: Spammers Most Likely Users Of E-Mail Authentication (TechWeb) by bfields
Parent article: Spammers Most Likely Users Of E-Mail Authentication (TechWeb)

> If people stopped sending bounces when they couldn't authenticate the from
> address, that'd cut down significantly on my "spam"

I just stopped accepting all mail from parties where I couldn't validate the from address. That elimitated about 70% of my spam. There's still a lot of spam sent with fake addresses.

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Spammers Most Likely Users Of E-Mail Authentication (TechWeb)

Posted Jul 15, 2005 15:16 UTC (Fri) by giraffedata (guest, #1954) [Link] (3 responses)

>I just stopped accepting all mail from parties where I couldn't validate >the from address. That elimitated about 70% of my spam. And plenty of your ham, too. Not many people hate spam enough to do that. In fact, you're most of the way toward the ultimate spam solution -- don't accept any mail at all.

Spammers Most Likely Users Of E-Mail Authentication (TechWeb)

Posted Jul 16, 2005 7:34 UTC (Sat) by dwmw2 (subscriber, #2063) [Link] (2 responses)

And plenty of your ham, too. Not many people hate spam enough to do that. In fact, you're most of the way toward the ultimate spam solution -- don't accept any mail at all.

Not really. You don't lose much ham by rejecting mail which has an invalid reverse-path, and in the cases that you do it tends to improve the actual communication.

Consider an analogy... if you are sending me a letter by snail mail and you accidentally put an invalid return address on it, how am I ever going to reply or actually manage to have a conversation with you? It's much better for that letter never to leave your local post office where your postie knows you and will hand it back to you.

That's basically what happens when my mail servers reject a mail from an invalid recipient. Most of the time it's actually spam, and the spambot just moves on to its next victim. But on the rare occasion that it's actually a genuine mail from someone who has misconfigured their mailer, the fact that I reject their mail means that their own mail server can tell them about it. If I'd accepted the mail, that chance for them to fix the problem would have been lost.

Spammers Most Likely Users Of E-Mail Authentication (TechWeb)

Posted Jul 16, 2005 17:44 UTC (Sat) by giraffedata (guest, #1954) [Link] (1 responses)

I guess you're talking about a different kind of validating the from address.

The context of this article is SPF, which is about determining that a From: address in an email, while it may be a valid email address, is not the address of the person who sent the email.

But while SPF provides a way to prove the From: address is genuine, most ham doesn't participate in SPF, so one wouldn't want to reject mail just because SPF failed to validate the from address.

Spammers Most Likely Users Of E-Mail Authentication (TechWeb)

Posted Jul 18, 2005 7:54 UTC (Mon) by farnz (subscriber, #17727) [Link]

SPF validates the "MAIL FROM:" part of the SMTP protocol. Unlike Sender ID, it has nothing to do with the "From:" header of the mail message.

A compliant SMTP server is supposed to return bounces (not rejects) to the address given in "MAIL FROM:"; spammers don't want bounces, so they tend to use false addresses in "MAIL FROM:", while legitimate users do want bounces, so they use genuine addresses in "MAIL FROM:"