Of course it all started with spam. But the response was just as destructive. I worked for a small ISP (25K email customers) back in the mid-2000s, and it was

Of course it all started with spam. But the response was just as destructive. I worked for a small ISP (25K email customers) back in the mid-2000s, and it was so hard to keep email flowing. All it took was one random customer somewhere on our DSL who had a misconfigured open relay, and spamhaus would blacklist us. They wouldn't respond when we'd try to get the block lifted. We tried and tried to work with them to streamline the process, nobody wanted spam to go through our servers, but they weren't really interested in any cooperation. They were perfectly happy to stop all legitimate email if it stopped a single spam. I don't work there any more, but I'd be surprised if that little ISP hosts their own email servers nowadays. It's so expensive to deal with such issues, it's just not worth it.