Chris-Linfoot.net

• Obviously, the relative performance of DNSBLs depends upon the order in which they are queried. Aggressive lists (e.g. SORBS), queried first will tend to reduce the apparent effectiveness of other lists - but that does not mean that the other lists are less useful.
  
• The graph is on a logarithmic scale simply because the gap between the highest performing lists and the lowest is two orders of magnitude and cannot readily be represented on a linear scale.
  
• The top performers here are (no real surprises) SORBS, DSBL and our local list -- the local list was the top performer prior to Intercept (Intercept changed this by querying DNSBLs before looking at locally blocked names) and it will be again once ND7 goes live here (because of the way IP and host name blocking and whitelisting works in ND7). In fact, these three lists alone block over 80% of our spam.
  
• Spamhaus (the combined sbl-xbl zone) is in the position it occupies mainly because it is largely pre-empted by SORBS and our local list. But it remains an essential and trusted line of defence.
  
• Spamcop and Blackholes.us continue to provide a valuable backstop against abuses that slip past the others; Spamcop because of its dynamic, near real time behaviour and Blackholes because we know we never want email from a small number of countries/ISPs which, although heavily blacklisted elsewhere, still have a large allocation of un-blacklisted addresses.
  
• ORDB has blocked the smallest amount of spam of any DNSBL here for the past few months, probably because a) it lists only simple open relays and b) most of these are also listed by at least the DSBL and in many cases also SORBS.

So, what does this mean for you? Well, it re-enforces my earlier advice. If you have access to whitelisting capability (and if not now, you will have with ND7), then you should seriously consider SORBS. DSBL remains a very powerful and fairly safe list to use even if you have no whitelist. So does Spamcop in fact. Spamhaus remains an effective list and is the safest of all with regard to false positives. Tactical use of Blackholes.us zones may benefit some sites (some trial and error required).

And if you don't have a local list, think about starting one.

Category: Spam Statistics
Technorati: Spam Statistics

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