Author: H.User1325 (12 Jan 13 10:52am)
I didn't respond before because with the information given I don't know how to help you. Keep in mind I am JUST a contributor to PHP and user of http:BL service.
http:BL does not block anyone. http:BL returns information about the IP address submitted that is then used by your application to decide what to do. Did you install a package like Spam-o-matic or ZB Block? To make sure a new user sees an affect, the blocking threshold is by default set vary low, like 1 or 5. This may be to low for your application. You could check the control panel and change the setting.
For my implementation I have the rejection level set so that any IP with a http:BL threat level higher that 30 is blocked. At this level I get no false positives and only about 10% of the spammers get through. Sense all new members are monitored, no one but me sees the first (and only) spam they post before being banished.
I sympathies with your users that must use an ISP that also supports spammers. My sympathy extends only to those that don't have an option of providers; realizing there are places in the world with limited connectivity. I suggest they find another ISP or raise hell with their provider.
Better ISPs monitor their users and in self-defense, identify infected users and help them remove the infections. This not only protects the reputation of the ISP, it also provides better service to all of their customers.
Mind you the way you pleaded your case you made it sound like it is PHP's fault that some people let their computers get infected and add to the level of spam or that some ISPs are not aggressively policing their part of the internet to prevent spam.