MarkOly - 8:16 pm on Feb 21, 2013 (gmt 0)
As far as the major blacklists, like Spamhaus, I know they work off IP. Defintely the IP of your host's mail server. And maybe the IP of the originating computer, found in the email's header.
As far as Gmail, Yahoo, etc, they have their own rules for spam filtering. They definitely use the blacklist reports. And I think they also combine other things - like domain, possibly - and possibly the results of their SPAM / NOT SPAM buttons.
For awhile, I had the worst time getting my emails thru to Gmail. I couldn't figure out what they were using to classify my emails as bad. My host's email server wasn't blacklisted. My personal Roadrunner IP was on one blacklist. But it's always on a blacklist, no matter how many times it changes. So I think there's something else. I wonder how much effect the SPAM / NOT SPAM buttons have. I couldn't help but to think that maybe a few people went thru their entire email folders, clicking SPAM on everything, including my emails. At one point, when I would take a phone order from somebody with a Gmail address, I would tell them to check their SPAM folder for order confirmation. And oh yeah, "Do me a favor and click the NOT SPAM button." Not long after that, the Gmail problem went away. I'm sure that was just a coincidence though. Anyway, I would love to know how many SPAM clicks it takes to get you blacklisted on Gmail. And how many NOT SPAM clicks to take you off. I bet it's less than you would think.
I'm always checking my host's email server for blacklisting. As soon as it's blacklisted, I send my host an email to let them know. Within a day, it's usually off the blacklist.