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

Would SOPA and PIPA bills 'break Internet?' Anti-piracy measure being revised

Call it – the Internet strikes back.

Read more...

---

The most dangerous remaining parts of SOPA and PIPA

SOPA, in its original form, is all but dead. The White House spoke up last weekend, saying that it would oppose (veto) any legislation that reduces freedom of expression, increases cyber security risk, or undermines innovation on the global Internet. However, as heroic as the rhetoric may sound to proponents of internet freedom, these bills [...]

Read more...

---

SOPA Getting a Face-Lift: How Evil Will It Be?

The House version of the Stop Online Piracy Act, the proposed anti-piracy legislation that drew a planned and widespread internet revolt Wednesday, is likely to undergo a radical overhaul to muster passage, a House aide said Thursday. But it's too soon to say what might be amended. The chorus of lawmakers who now say they oppose the measures have not publicly itemized their objections.

Read more...

---

A Useful Primer On The Internet Blackout And Why Wikipedia Is Going To Bat Against SOPA

The internet is a strange and mysterious place today. I keep forgetting Wikipedia is down and going over there to look up this or that subject. Then I?m reminded that no, Wikipedia and Reddit and Craigslist and many other sites have gone black to protest the anti-piracy bills SOPA and PIPA. Over at Wired David ...

Read more...

---

Don't let big business break the internet

Legislation on internet piracy presented to Congress last year is the typical kneejerk response of the 'content' industry to change The key to survival – in business as in the jungle – is to be able to learn from your mistakes. The strange thing is that some industries haven't yet figured that out. Chief among them are the so-called "content" industries – the ones represented by huge multimedia ...

Read more...

---