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

Block List News

Block and Company Releases the“My Block Power Suite”

(PRWEB) February 3, 2010 -- Have a bank with multiple locations that purchase products? Need a simple yet effective way to see and manage the order requests from these multiple locations? The My...

METTLER TOLEDO Introduces an Affordable Reaction Block for Solid Phase Peptide Synthesis (SPPS)

Columbia, MD (PRWEB) June 21, 2009 -- Peptide libraries are widely investigated and routinely screened for their drug-like properties. Synthesis using resins or solid supports is a favorite route...

NKC board decides to stick with block schedule in high schools - Kansas City Star

WSAU

NKC board decides to stick with block schedule in high schools Kansas City Star The list of possible cuts includes nearly $9.5 million in possible reductions; however, Tuesday's discussion centered mainly on health services cuts. ... Four directors added to school district's list of changesMorgan Hill Times PSUSD Opts for Teacher and Staff LayoffsKPSP Local 2 Walnut Creek district cuts $1 million from budgetSan Jose Mercury News all 150 news articles »

AIPAC calls for swift action to block US companies supporting Iran - Jewish Telegraphic Agency

Reuters

AIPAC calls for swift action to block US companies supporting Iran Jewish Telegraphic Agency The enhancement measure would require the Government Accountability Office to publish a list of potential sanctions act violators every month, ... EU, US concerned about Iran's nuclear activitiesLas Vegas Sun all 654 news articles »

Wednesday crime log - Midland Daily News

Wednesday crime log Midland Daily News 11:38 am -- Items in the 4500 block of North Saginaw Road were damaged. 11:43 am -- Police were called to the Law Enforcement Center to investigate a report ... and more »