What is a dot-zero listing?

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Some email blacklists focus solely on allowing their users to block mail from problematic sources. Others aim to reduce the amount of bad mail sent and prefer senders clean up their practices, rather than just blocking them wholesale. The Spamhaus SBL is one of the second type, using listings both to block mail permanently from irredeemable spammers and as short term encouragement for a sender to fix their practices.
All a blacklists infrastructure – and the infrastructure of related companies, such as reputation monitoring services – is based on identifying senders by their IP addresses and recording their misbehaviour as records associated with those IP addresses. For example, one test entry for the SBL is the IP address 192.203.178.107, and the associated record is SBL230. Because of that they tend not to have a good way to deal with entities that aren’t associated with an IP address range.
Sometimes a blacklist operator would like put a sender on notice that the mail they’re emitting is a problem, and that they should take steps to fix that, but they don’t want to actually block that senders mail immediately. How to do that, within the constraints of the IP address based blacklist infrastructure?
IP addresses are assigned to users in contiguous blocks and there’s always a few wasted, as you can’t use the first or last addresses in that range (for technical / historical reasons). Our main network consists of 128 IP addresses, 184.105.179.128 to 184.105.179.255, but we can’t put servers on 184.105.179.128 (as it’s our router) or 184.105.179.255 (as it’s the “broadcast address” for our subnet).
So if Spamhaus wanted to warn us that we were in danger of having our mail blocked, they could fire a shot across our bow without risk of blocking any mail right now by listing the first address in our subnet – 184.105.179.128 – knowing that we don’t have a server running on that address.
For any organization with more than 128 IP addresses – which includes pretty much all ISPs and ESPs – IP addresses are assigned such that the first IP address in the range ends in a zero, so that warning listing will be for an address “x.y.z.0” – it’s a dot-zero listing.

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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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Spamhaus changes

A number of ESPs are reporting an increase in SBL listings of big, well known brands. InterestingSBLs seems to confirm this.
Just on the month of June I see tweets reporting SBL listings for: Disney (again, and again) AAA Michigan, NRCC, the Mitt Romney campaign, Macy’s (again) Facebook, Walmart Brazil, Safeway, Bacardi.
What happened? I think there are a number of reasons for an increase in SBL listings of well known brands.
The first is that botnets are rapidly becoming a solved problem. That’s not to say that they’ve gone away, or that we should stop being vigilant about the spam and malicious mail coming out of them, but that there are more and better tools to deal with botnets than there have been in the past. That means that the folks at Spamhaus can look at different classes of unsolicited email.
I believe Spamhaus has some new mail feeds that let them see mail they were previously not seeing. Anyone who has multiple email addresses can tell you that the type of spam that one address gets is often vastly different than the type of mail another email address gets. When dealing with spamtrap feeds, that means that there is unsolicited mail that isn’t seen by the feed. I know there are companies who claim to have lists of hundreds of thousands of spamtraps, and I don’t doubt that some enterprising spammers have discovered Spamhaus spamtraps in the past. Adding new feeds means that Spamhaus will see spam that they were previously missing due to their traps being compromised.
As well as bringing up new feeds, I suspect Spamhaus has better tools to mine the data. This means they can see patterns and problem senders in a clearer way and list those that meet the Spamhaus listing criteria.
I’m not saying the Spamhaus standards have changed. Spamhaus has always said they will list anyone sending unsolicited bulk email. But, as with many organizations what they could do was limited by the available resources. That resource allocation has changed and they can deal with more senders.
What does all this mean for senders? In a perfect world it wouldn’t mean anything. Senders would actually be sending mail only to people who had asked to receive it. Senders would have good list hygiene and pull off abandoned addresses long before they could be turned into spamtraps.
But we all know this isn’t a perfect world. There are a lot of senders that have lists with years of cruft on them. And not all of those addresses on the list actually opted-in to receive that mail. Many of those senders have good stats, decent opens, low unknown user rates, and low complaint rates. But that doesn’t mean there aren’t problems with the lists. And those hidden problems may mean that just because you haven’t had a Spamhaus listing in the past doesn’t mean there isn’t going to be one in your future. It means senders who want to avoid SBL listings need to pay attention to list hygiene and dead addresses. It means the source of addresses and their audit trail is even more important than ever.
Meanwhile, ESPs are struggling to cope with the ongoing and increasing SBL listings.
EDIT: Mickey attributes some of the increase in listings to Spamhaus being better able to detect appended lists.

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Spamhaus rising?

Ken has a good article talking about how many ESPs have tightened their standards recently and are really hounding their customers to stop sending mail recipients don’t want and don’t like. Ken credits much of this change to Spamhaus and their new tools.

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