Hosting spammers (and ignoring pleas for assistance in stopping them or refusing to kick them off) is another way to get onto one of these filter lists. And still a third is to host sellers of "spam tools." Because the IPs of the service providers themselves get blocked, anyone using legitimate, non-spamming services hosted on these IPs is also blocked.

I did quite a bit of research on this this summer, so I'm certain of the above. Also, there are quite a number of these online filter systems, however Mailwasher uses two open relay databases (ORDB [relays.ordb.org] and VISI [relays.visi.com]) and the Spamcop list - bl.spamcop.net.

It shows what was used to judge whether to blacklist an email automatically.

As an added tidbit, China seems to be the leading "open relay" country to the extent that many hosts simply block any mail coming from there. These hosts report having little success in getting the Chinese to help by setting up their email servers correctly.

China is on my server's "block" list, and Japan is quickly earning a spot there. Much of the email I get from myself (yeah, right) originates at a Japanese server.

Marye