Earthlink Deploying Challenge-Response Anti-Spam System

deliasee writes "The Washington Post reports that Earthlink is preparing to offer new spam filter technology that requires sender authentication. AOL is still concerned that such technologies will put too much burden on consumers." The day after it's deployed, every legitimate mailing list on the planet will get challenges from all the Earthlink subscribers...

Comments

Correction

[robbyjo]

every legitimate mailing list on the planet will get challenges from all the Earthlink subscribers

Not exactly right. It happens only for the first time to detect whether the sender is legitimate or not. Quote the article:

The system automatically recognizes future e-mails from the same sender, so the verification needs only to be performed once.

The problem with this system is that the spammer can still spam using legitimate e-mail accounts as a camouflage (or expired e-mail accounts). Once the legitimate e-mail address is procured, the spam still goes on. It is futile, IMHO.

It can work - if implemented correctly

[dracol1ch]

I've been using Mailblocks since they opened publicly. I can't speak for the implementation that Earthlink is planning on utilizing but the Mailblocks system works very well.

First it is important to note that the challenge system at Mailblocks is not something that can be automatically replied to. Much like the signup verifications for many forum systems out there the Mailblocks challenge email is simply a link to a web site. On that web site is a dynamically generated .gif of a number. The image is formatted in such a way so as to make it difficult for screen scrapers to write an algorithm which can decipher the numbers in the image (multiple fonts, different colors, background noise). If ever a spammer figured out how to programatically decipher the image then Mailblocks simply has to rework their image generation system and stay one step ahead of the spammers.

Next you have throw away addresses. Maiblocks calls these trackers. When you create a tracker a number and short ID are appended to the end of your username. This email address is then immune to the challenge response and can either be delivered to a purpose built folder or directly to your inbox. So if you wanted to have an address to get receipts from you simply make a tracker named say [username]+receipts4325@mailblocks.com. Then any email to this address can be delivered to the +receipts folder in your inbox. If you start getting spam at that address you just delete the address and create [username]+receipts5563@mailblocks.com and start giving this out. It can be a little bit of work to maintain your trackers but compared to deleting 20-30+ spam mails from my accounts each day it's well worth it.

When an email is successfully delivered to your main address the originating address is entered into your address book including the reason why this address was validated (completed puzzle, user added). Mailblocks also adds the address of any outgoing mail you write to your address book so that responses can be properly delivered without challenge. Finally, if you are expecting something to appear in your email that doesn't the 'pending' folder holds all email that hasn't been validated for a certain amount of time before deleting. If you really want to you can go back and dig through the email there to find the one you want, validate it, and it will be delivered to your inbox. If something gets validated you don't want simply go to your address book and either delete it or check 'do not deliver mail from this address'. Viola. Also of interest is the fact that Mailblocks can provide the same security to any other mail account you have. It can check POP3, IMAP, accept forwards, and even screen scrape web mail to bring all of your mail to a central location. When it does it provides the same callenge-response capability through these other accounts.

Re:You can do this yourself.

[StarOwl]

I use TMDA to provide a challenge/response mechanism in my antispam filter.

When I first started using TMDA, I had problems with people not understanding the mechanism. My grandmother, for example, complained about "bounces" (how she interpreted the challenges).

So, to avoid those problems, I:

• Actively manage my whitelist. For example, if I needed to send a resume, I would make darned sure that the prospective employer's domain was on the list.
• Use challenge-response only in conjunction with other antispam tools. My system is roughly: if I know it's spam (tagged address known to be in spammers databases), it gets trashed. If spamassassin or spamoracle thing it's spam, I refer to tmda for possible challenge/response. Otherwise, the mail gets delivered.
• Warn people about the system. If I know that someone new is about to send me email, I warn them: "You might get an autoresponse back. If you do, just hit 'reply'."
• Use some care in writing the challenge email. Trying to craft a letter that is understandable to non-geeks wasn't that easy.

I still have the odd piece of spam leak through that process, but it's nowhere near the quantity that's actually sent to me.

The only problem with the scheme: there are some spammers who are dumb enough to not get the hint, and respond to the challenge. They don't seem to realize that their response probably constitutes harassment via 'net, which is a crime in the U.S. (Spammer go to jail. Do not pass go. Do not collect $200.)

Re:You can do this yourself.

[BlackHawk-666]

I also use TMDA and I can tell you it has vastly reduced the amount of spam I receive from approximately 20-30/day to 1 in the last two months. I've never been happier ;-)

Whitelisting is important, and easy too. Just export your address book to a text file and copy the results to your whitelist (which is also text).

It's worth noting that you can also auto-whitelist anyone you send mail to by using their nifty little mail proxy. It sits and proxies for SMTP and adds all outgoing mail automatically to your whitelist, so whoever you sent that resume to will never see a challenge...neat!

P.S. Can't recommend the product enough.