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Things You Should Know Before Using DNS Block Lists
DNS block lists are easy to include into most mail servers. They are a very effective and efficient server side tool to help keeping spam out of your systems. As the name implies they use domain name servers to transmit the information whether mails from a distinct mail server should be accepted or rejected.
Sometimes they are too effective. It can happen that a mail server is listed on a block list wrongfully. This can lead to a situation where your mail server will reject mails that you wanted to receive. The biggest problem with block lists is that you have to trust somebody else to take the right decision which mails to accept and which ones to reject.
So how useful are DNS block lists after evaluating the pros and cons? They can be very useful to lower the overall CPU usage of your anti spam strategy. It is advisable to use a small number of carefully chosen blocklists. If you are using a block list, subscribe to the mailing list or newsletter of the organization who runs the block list. That way you will take note of any problems that the block list may have and you will be informed if it gets shut down. DNS blocklists should never be your only strategy against spam. They should be combined with other mechanisms to help keeping spam out of your inbox.
There are some things you should consider before implementing DNS block lists in your anti spam strategy. If you reject a connection from a mail server because it is listed in a block list, return a detailed error message. This enables the admin of a mail server that gets listed wrongfully to see why the mails get rejected and to act accordingly.
If your mail server software allows to select the order of different sender or client restrictions be sure to put DNS blacklists after SMTP authentication. This enables your co-workers (and your customers if you are in the ISP business) to send their mails even if they come from a dial-in IP address that is listed in a block list.
You should consider using DNS block lists for scoring instead of blocking if your mail server has enough resources (CPU, IO, traffic). That would mean to use the block lists in a program like spamassassin that gives points for different criteria of a message and considers it as spam if it surpasses a certain number of points. That way the chances for false positives are lower because a message is not rejected if the sending server is on a single block list only. The message will get rejected if there are other signs of spam.
Huge indexes of available DNS block lists can be found at www.moensted.dk/spam/ and www.declude.com.
Spam Videos
Dns Block List News
Kaminsky DNS Bug Claimed Fixed By 1-Character Patch - Slashdot
Kaminsky DNS Bug Claimed Fixed By 1-Character Patch Slashdot - An anonymous reader writes "According to a thread on the bind-users mailing list, there is nothing inherent in the DNS protocol that would cause the massive ... |
Black Hat: DNS Flaw Much Bigger Than Thought - CRN
Black Hat: DNS Flaw Much Bigger Than Thought CRN, NY - But that's far from a complete list of the systems that could be affected, and Kaminsky repeatedly used the term "domino effect" in describing the ... Black Hat: DNS Researcher Flaw Much Bigger Than Thought Net address bug worse than feared Kaminsky covers DNS at Black Hat – patch now or suffer |
28-08-2008: MCMC clamps down on Malaysia Today website - The Edge Daily
28-08-2008: MCMC clamps down on Malaysia Today website The Edge Daily, Malaysia - Simply put, a DNS black hole list is a means by which an Internet website may publish a list of IP addresses that people may want to avoid, and this list is ... |
Satan Is Still on My Friends List - InternetNews.com
Satan Is Still on My Friends List InternetNews.com - Security researchers Nathan Hamiel and Shawn Moyer took the stage at Black Hat here today to explain to attendees how easily various social networks could ... |
New exploit poisons patched DNS servers, claims researcher - Computerworld
New exploit poisons patched DNS servers, claims researcher Computerworld, MA - In a presentation at the Black Hat security conference last week where he outlined the flaw and provided more information, Kaminsky noted that others had ... |
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