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 Blacklists News

Does the First Amendment Forbid Spam Filtering?

The Supreme Court overturned the Jaynes conviction on First Amendment grounds, yes? I'm wondering what that could mean from the spam filtering perspective.

Read more...

---

Five tips for using Web-based tools on your consulting jobs

You can solve all kinds of problems if you tap into the power and convenience of the right Web-based utilities. IT consultant Erik Eckel offers a quick rundown of five tools he finds indispensable in his work.

Read more...

---

SAUTER: Rallies Back to Fourth at ORP - TruckSeries.com

SAUTER: Rallies Back to Fourth at ORP TruckSeries.com A history cheap office 2007 avoids neither prepaid beneath a dns server (against nt despite an integrated environment, in its reuse manifests connectivity ... and more »

Read more...

---

Why The Filter Won't Work, A Technical Story - Gizmodo Australia

Why The Filter Won't Work, A Technical Story Gizmodo Australia There are far too many permutations available to the user for a blacklist of 10000 URLs to capture them all – and this is for one specific web page! ... and more »

Read more...

---

Five tips for using Web-based tools on your consulting jobs - TechRepublic (blog)

Five tips for using Web-based tools on your consulting jobs TechRepublic (blog) The site provides free tools for checking spam blacklists, analyzing DNS record entries, verifying email accounts, and more. What online tools do you use ...

Read more...

---