This is why it is *very* important to understand what spam databases list before using them.It looks like blackholes.us is listing complete ISP's regardless of offending ip's.
There are lots of companies that will lose large amounts of legitimate mail by using some of the blackholes.us spam databases. On the other hand, there are quite a few companies that will find that only spam gets caught by those tests.
The key to the blackholes.us tests is that there isn't anything "magical" about them -- each one performs a certain task, and should be able to do so with 100% accuracy. Some of their tests list IP addresses of some countries that tend to send out a lot of spam, others list ISPs. The tests that list countries is designed to catch mail from those countries regardless of whether or not it is spam, and the ISP tests are designed to catch mail from those ISPs -- again, regardless of whether or not it is spam.
The best way to implment the blackholes.us tests are [1] Only use the tests that are appropriate for you, and [2] Use them in a weighting system. For example, we could never block E-mail based on the country, as we have customers in many countries. However, we get a lot of spam from China (and have few customers there), so we could assign a heavy weight to the China test.
Also note that the next beta of Declude JunkMail will include an experimental way of identifying the countries that the E-mail passed through, which will be less resource intensive than the blackholes.us tests.
-Scott
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