eXploits Block List (XBL)
Policy Block List (PBL)
If you are a UCAR user and you want to read about how you can enable or disable spam blocking for your own mailbox, go here.
You may have been referred here by an error message from our mail server. Unfortunately, the network or domain through which you sent your mail is on one or more of the sets of lists our users can individually select to help protect their mailboxes against the steadily rising tide of spam they would otherwise receive.
All mail coming into our mail servers that is coming from comprmoised systems or non-server home networks is rejected unless it is authenticated with SMTP AUTH first.
At their option, our users can employ an additonal filter that also blocks mail from spam friendly systems
Misconfigured systems are those that allow promiscuous connectivity from spammers seeking to hide their origin or amplify their spam sending rate. These systems, by their detectable actions on the net, are known to be compromised and under active control by spammers. Blocking mail from misconfigured systems does risk that some legitimate mail may be blocked as well. However, misconfigurations that lead to open relaying or proxying can and should be repaired. Systems that have been compromised by spammers should have the holes that are allowing them to be used by spammers closed. Once the necessary repairs are made, the listings can be removed, and all mail from the fixed systems will flow freely again.
Spam friendly systems are those that participate in sending spam, providing spamware, or providing havens for spammer resources. Our users who block mail from spam friendly systems realize that they may block more legitimate mail than they would if they were just blocking mail from misconfigured systems. However, their spam load is great enough that they have simply had to opt for more protection. They also realize that, once a provider stops providing a spam injection or haven service, the spam friendly listings can be removed and legitimate mail from the reformed network will flow freely again.
You have a couple options for getting a blocked message through to an individual UCAR user who has elected to turn on spam blocking. They are, in decreasing order of what is best over the long term for both you and the Internet:
In order to fix the problem, you need to know which lists your sending system is on. Please visit the specific URLs referenced in the bounce message you received, or see the URL for the relevant block list in the specifics section below. Follow the instructions at the relevant block list site for getting your network or domain cleaned up.
If you are unsure of which one has you listed, or suspect your system or network may be listed by more than one, you can query many block lists at once using one of these convenient lookup services:
Once you have fixed the problem that has your network or domain listed, you will again be able to get your mail through to our users who have chosen to turn on spam blocking.
Even better, after you fix the problem you will also be able to get your mail through to other organizations that use the same lists. That consolidation feature is why we use the shared lists we do, rather than maintaining our own. Instead of requiring you to contact hundreds of individual list maintainers, this instead gives you a few well known places to go to get unlisted.
However, if you can't clean the problem up (perhaps because the only ISP in your area is TPC [the phone company] and you lack the leverage to get it to behave in a more neighborly manner), you still have a couple options.
You may be able to reach your correspondent by sending through a different mail server that is properly configured, or that isn't on a spam friendly network.
If that fails, you should contact the person you're trying to reach out of band (via telephone, or perhaps postal mail), and ask them to let your mail in anyway. They can do that by turning off or lowering the level of their spam protection.
Keep in mind first that block lists on the Internet come and go for various reasons. As a result, it is going to be difficult to keep this section of this web page up to date all of the time.
The compromised systems and home systems filters have been approved for use against every incoming mail connection by the Computer Security Advisory Committee (CSAC) which sets security policy for UCAR. Like most other sites on the Internet, UCAR has been innundated with spam, and we have taken an increasingly aggressive stance against it, even at the risk of occasionally blocking legitimate mail. Our default filters are designed to be as conservative as possible while still being reasonably effective.
Please note again that UCAR users individually choose to turn on the spam-friendly systems blocking for their addresses. The UCAR postmaster does not override an individual user's decision.
The default misconfigured systems filter includes the following DNS-based block lists (dnsbls):
Please keep in mind that the above services do not themselves block any mail. Rather, UCAR specifically elects to use the services as advisories for their own individual blocking.
The spam friendly systems option some of our more hard-pressed users select includes the following additional DNS-based block lists (dnsbls), on top of the previously mentioned misconfigured system option:
Again, please keep in mind that the above services do not themselves block any mail. Rather, our users specifically elect to use the services as advisories for their own individual blocking.
About Korea Services: It should be noted that UCAR does not harbor any ill will towards the country or people of South Korea, and indeed we work with colleagues from that country. But the ISP's in South Korea make a lot of money from their spammer customers, and use their regular customers as "human shields" for their lucrative spammer customers. They make it intentionally difficult to block only the spam without also blocking some legitimate non-spam customers. All this said, we have found that blocking mail from South Korea to users here who do not need to receive it cuts down significantly on the amount of spam we receive. If you are in South Korea and need to get mail to UCAR colleagues, the only way that can be done is to get the UCAR user to turn off the aggressive spam blocking filter.
There are additional services used from time-to-time for users that have selected agressive spam blocking. These change frequently and so are not documented here.
We have recently added a filter that blocks mail from "home" networks. More and more spam originates from "botnets", or networks of compromised home systems controlled by a central server. Home systems are infected with a "spambot" virus that "phones home", allowing the spammers to control the home system and use it for sending spam. Blocking home systems from sending directly to UCAR's mail servers is thus a very effective way to cut down on botnet spam.
Legitimate users on home networks are expected to use a designated mail server provided by their ISP to send mail, rather than sending directly from their home systems. UCAR provides such a server for our staff to use; it requires use of SMTP AUTH to authenticate the user, then the usual spam filters are bypassed. If you are a UCAR user, your local desktop support group can help you configure your mail client to use SMTP AUTH.
In closing, let us just say that we are very sorry our user must refuse mail from your ISP's or organization's open proxy, open relay, dynamic dialup, or spam origin & support domain or network. We look forward to a day when using such lists are unnecessary; when spammers are no more.
Thank you, and good luck with your future email endeavours.
