January 19, 2016 ESP Issue
Early today, a number of high volume ESP mail servers were listed.
As soon as this was discovered, they were purged from the list.
Background: recently a few new traps were incorporated into the
CBL. From the beginning these traps were behaving very strangely,
and during the process of trying to identify why, a bug was introduced
and caused the ESP listings to occur.
CBL remediation: as soon as this was discovered, the listings were
purged, and the bug corrected. However, analysis of the issue
raises issues with the ESPs in question.
Affected server analysis: The listed servers all send extremely
high volumes of email to domains that have never existed. Clearly,
closed-loop confirmation is not being used by these senders, and
they have no list management processes implemented (eg: removing
Furthermore, each of the servers were using an abusive technique
to "hold the SMTP channel open" even when there was no email to
send, thus unnecessarily wasting recipient resources (in some cases
to a very high degree) - in effect, a resource-starvation DoS attack
Recommendations: ESPs affected by these listings should review their
inadequate list management, non-existent opt-in confirmation policies
and stop using artificial "hold channel open" techniques. These
are abusive practices, no question about it, and ESPs are at high
risk of being blocked by recipients entirely aside from the CBL or
I'm listed, what do I do?
The CBL has easy self-removal. See:
CBL Lookup AND Removal
It will provide you with information on why the IP was listed, how
to correct the problem that caused the listing, and
a link to do self-removal.
The rest of these web pages are intended to help you understand
what could cause a listing, and how to diagnose/remediate the problem.
The CBL expects you to resolve the problem, preferably before you
do a delisting.
If you simply delist without resolving the problem, it will almost
certainly list again.
Of late a lot of people are emailing us and simply asking us to delist
an IP address.
We can't do it more quickly than you can.
It's a LOT faster if you do it yourself.
What is the CBL?
The CBL takes its source data from very large mail
server (SMTP) installations.
Some of these are pure spamtrap servers, and some are not.
The CBL only lists IPs exhibiting characteristics which
are specific to open proxies of various sorts (HTTP, socks, AnalogX,
wingate, Bagle call-back proxies etc) and dedicated Spam BOTs
(such as Cutwail, Rustock, Lethic, Kelihos etc) which
have been abused to send spam, worms/viruses that do their own direct
mail transmission, or some types of trojan-horse or "stealth"
spamware, dictionary mail harvesters etc.
The CBL does not list based upon the volume
of email from a given IP address.
The CBL also lists certain portions of botnet infrastructure, such
as Spam BOT/virus infector download web sites, botnet infected machines,
machines participating in DDOS, and other web sites or name servers
primarily dedicated to the use of botnets.
Considerable care is taken to avoid listing IP addresses that are shared
or are likely to be shared with legitimate use, except in the
case of infector download websites, phish emission or DDOS.
Our botnet detections may not necessarily directly involve the
observation of spam emission, but most botnets are at least occasionally
involved in email spam, in addition to infostealing, DDOS attacks etc.
In other words, the CBL only lists IPs that have attempted email
connections to one of our servers in such a way as to indicate that
the sending IP is infected with a spam-sending virus or worm, acting
as a open proxy for the sending of spam, OR, IPs primarily used in
the operation of botnets
The CBL does NO probes. In other words, the CBL
NEVER makes connections to other machines to "test" anything.
The CBL does NOT test for nor list open SMTP relays.
The CBL only lists individual IPs, it NEVER lists ranges.
The CBL does NOT care whether an IP is dynamic or not,
if connections the IP makes indicate that it's infected, it is
The CBL does NOT attempt to associate IP addresses to
persons or organizations, and furthermore, a CBL listing
should NOT be construed as accusing anyone of spamming -
virtually all listees are the victims of a virus or other compromise, not
The CBL does NOT accept external submissions for listing.
Hence it is not possible for the CBL to be used as an instrument of
revenge (eg: "disgruntled ex-employee" or "competitor").
The CBL operates in an entirely automated way designed to avoid
listings due to bounces of forged spam, virus
bounces, and "real" mail servers emitting the occasional spam.
However, in some circumstances severe mail server misconfiguration
can make it look as if a mail server is infected.
It does not attempt to list every possible spam source.
This list is based on information believed to be reliable. No
warranty is made that it is accurate or complete.... Use entirely at
your own risk.
There is no supporting data or "evidence" file available for any given
listing, and no mechanism to ask why any given listing took place. To
counteract this, there is an automated no-questions-asked removals
procedure allowing any affected party to delist a specific IP address
rapidly. However, delisted IPs are relisted if new evidence of spam
activity is subsequently detected.
Entries automatically expire after a period of time. The approximate
detection time of a specific entry can be obtained from the web
What to do if you're listed/How do I get delisted?
Use the lookup tool it will
often give you further detail.
It gives the link to the delisting tool.
See the FAQ for more information on
how to identify and resolve a CBL listing.
How to use the CBL
Before using the CBL, you should read our
terms and conditions.
The CBL can be queried in the usual way for DNS-based blocking lists,
under the name cbl.abuseat.org.
Entries in the CBL are returned with an IP address (always 127.0.0.2) and
a TXT record containing a link to the lookup/removal pages.
If you wish to run a local server using the CBL data you can download
the CBL zone. Please see our FAQ under the
subject "How do I download the CBL as a list of IPs?"
We're getting a lot of reports of spurious blocking caused by sites using
the CBL to block authenticated access to smarthosts / outgoing mail servers.
THE CBL is only designed to be used on INCOMING mail, i.e. on the
hosts that your MX records point to.
If you use the same hosts for incoming mail and smarthosting, then you
should always ensure that you exempt authenticated clients from CBL checks,
just as you would for dynamic/dialup blocklists.
Another way of putting this is: "Do not use the CBL to block your
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