> The filtering behavior reported here is either misunderstood or misrepresented. First, no, no major ISP (Gmail, Yahoo, Microsoft/Outlook, icloud) is going to permanently block an IP range; filters are designed to be dynamic. In severe, ongoing, high-volume spam scenarios, you could see a 2-week block, maybe occasionally 30 days. But never "one strike".

You say you're knowledgable, but I also ran my own email server for a couple of decades, and gave up for precisely this reason. Maybe this is even true, but when you're trying to get mail sent, YOU NEED THE MAIL SENT, and you can hardly wait 2 weeks or a month. Besides, your email server is going to give up and report it as undeliverable by that time. So you have to do the legwork to get off the block regardless of how long the "bigs" have the timeout set to. And that's happens so often, and is so onerous, it's not worth the hassle any more. Like many others here, I could have written this article.