More on spamfiltering feedback

Al wrote a post commenting on my post from last Thursday on spamfilters talking to senders who are being filtered. I think his take on it is close to mine. I would point out that Google has a pretty opaque system and no feedback to senders, but a lot of people seem to think their filters are accurate and do a good job.
Overall, I think there is room for discussion and feedback between senders and recipients, but on both sides the goal needs to be improving the enduser experience.

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Sender complaints about spamfiltering

JD posed a question in my post about Postini and trying to sort out a customer getting marked as spam by their filtering mechanism and I think it bears more discussion than can be done in comments.

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Yahoo and Spamhaus

Yahoo has updated and modified their postmaster pages. They have also put a lot of work into clarifying their response codes. The changes should help senders identify and troubleshoot problems without relying on individual help from Yahoo.
There is one major change that deserves its own discussion. Yahoo is now using the SBL, XBL and PBL to block connections from listed IP addresses. These are public blocklists run by Spamhaus. Each of them targets a different type of spam source.
The SBL is the blocklist that addresses fixed spam sources. To get listed on the SBL, a sender is sending email to people who have never requested it. Typically, this involves email sent to an address that has not opted in to the email. These addresses, known as spamtraps, are used as sentinel addresses. Any mail sent to them is, by definition, not opt-in. These addresses are never signed up to any email address lists by the person who owns the email address. Spamtraps can get onto a mailing list in a number of different ways, but none of them involve the owner of the address giving the sender permission to email them.
Additionally, the SBL will list spam gangs and spam supporters. Spam supporters include networks that provide services to spammers and do not take prompt action to remove the spammers from their services.
The XBL is a list of IP addresses which appear to be infected with trojans or spamware or can be used by hackers to send spam (open proxies or open relays). This list includes both the CBL and the NJABL open proxy list. The CBL list machines which appear to be infected with spamware or trojans. The CBL works passively, looking only at those machines which actively make connections to CBL detectors. NJABL lists machines that are open proxies and open relays.
The Policy Block List (PBL) is Spamhaus’ newest list. Spamhaus describes this list as

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Forgery and spamware

Recently there has been a massive uptick in forgeries. I have been seeing hundreds of bounce back messages, peaking at more than 1000 in an hour. I have been talking about this with people who monitor large spamtrap feeds, large MTAs and spamfilters and it seems this is not an isolated experience. The consensus seems to be that there is new spamware out there which is using email addresses on the spam list as a From: address
The volume itself is annoying. Thousands of messages a day from “mailer-daemon” telling me that the mail I sent with the subject line “Get a longer tool” cannot be delivered to some random address some where. These are coming to at least 3 separate email addresses. One of them was given to Intuit back in 2001/2002 when I registered a copy of Quicken, and ended up leaked to loan spammers and is all over spam lists. The other two are addresses scraped from websites. Same spammer has them, same spammer is using them as part of his spam run.
Even more annoying than the volume, though, is the challenge/response emails. “Your email to jobobjimbo@example.com cannot be delivered until you click this link.” I have been adding every domain I can find that is using c/r to my filters, and just discarding the c/r emails so I do not have to deal with them. That is not my ideal solution, it does mean that if someone using c/r ever tries to contact me I will not see the challenge and our communications cannot happen.
Some people have recommended that the right way to deal with challenges from forged spam are actually to answer the challenges. As the reasoning goes, if someone using c/r is going to outsource their spam filtering to a victim of spam forgery, then they should expect that the “spam filter” may have a different opinion than they do. While I always sympathized with this viewpoint, I was not sure I would ever confirm spam forgeries. The sheer volume of c/r stuff I have received in the last few weeks has almost convinced me that people who use c/r deserve every bit of spam they get. If a c/r filter lets in spam, then perhaps they will reconsider their choice to spew challenges out to forged email addresses.
The amount of c/r spam I am getting as part of the forgery runs is decreasing, I think I have finally managed to block the primary sources. It does mean I will not be able to communicate with people who use c/r in the future, but I find this a small price to pay for not having to be an outsourced spam filter. I get enough of my own spam, I really do not want to have to deal with yours.

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