Which consumer ISP blocks the least legitimate email? A complex question, partly due to the subtleties of what "legitimate" means. We’ve talked about this before.
One data point is the "deliverability" statistics captured by legitimate direct marketing email service providers (ESPs). Here’s some data from Return Path, showing a wide variation amongst different ISPs…
From this data (and remember it’s just one ESP’s data), people like MSN, AOL/Compuserve and Earthlink are doing relatively well. Road Runner, Comcast, and Verizon are examples of providers who leave a lot of legitimate email in the quarantine.
Thanks to Return Path’s Matt Blumberg for the idea.