Re: [exim] Spam filtering of blacklisted name serers

Tony Finch wrote:
> On Wed, 1 Oct 2008, Mike Cardwell wrote:
>
>> Marc Perkel wrote:
>>
>>> I'm having luck looking up the name servers of the sending host to see
>>> if it's blacklisted
>>>
>> But how accurate is it?
>>
>
> I did some similar experiments, and I found that it's not unusual for an
> email-oriented blacklist to catch a nameserver used for legitimate email.
> For example, a hosting service that has various dodgy web servers gets a
> /24 blocked which happens to include a nameserver which is not just used
> for the dodgy webservers but for various other well-behaved customers.
>
>

I'm not testing the IP of the name server. I'm looking up the host name
in a host name based blacklist. What it's catching is new "tasting"
domains that use existing blacklisted names for nameservers.