The problem is that a critical protection against large companies is via patents or at least the threat of. Without them, the ability to dethrone them becomes very limited.

Can you name an example of when a patent was used by a small company in the software industry to "dethrone" a very large company?

I'm having a hard time coming up with any examples; the lawsuits that come to mind are patent trolls, where the "little" company is a non-practicing entity so they can't be counter-sued for violating the giant's portfolio of patents. But, you sound pretty certain, so I want to figure out where I'm wrong.

Dethrone, no, but certainly sue for 100s of millions of dollars.

OK, can you name an example of that?

It's the whole point of patents. You want me to give you a list of patent lawsuits? :) Google is your friend.

I want an example of a case where a small software company successfully litigated a patent lawsuit against a huge company like Google, Microsoft, Facebook, etc. Preferably one where the instigator of the lawsuit was legitimately defending something novel and innovative. This is subjective, of course, and I tend to come down on the side of software not being something that should be patentable...but, it is patentable, so there are patents, so I'm asking: where are the lawsuits brought by small companies that are actually in the business they've patented and have sued a huge company?

You've made it sound like it happens all the time. I've been in the tech industry for two decades, and I can't think of any (though I'm sure they must exist). I assumed you had some cases in mind when you made the comment earlier, and I wondered what it was. I'm not demanding you go search for such a case. But, absent some sort of example, I'm gonna continue to assume it (almost) never happens.

Well, defending the company might entail getting acquired by another large company or NPA. I don't know of any examples where a small company sued a large one and continued to do business based on that lawsuit, but the threat of getting acquired certainly adds value to the company itself and discourages large companies from blatant copying.

Take that threat away, and small companies lose value and large companies copy without regret.

So, do you have an example of that?

Please don't violate the guidelines by rudely complaining about downvotes:

https://news.ycombinator.com/newsguidelines.html

Open sourcing the spam filter will only help spammers. It is unlikely that it would work on an individual server with small amount of traffic.

Instead of trying to make a perfect spam filter we should abandon outdated inreliable mail transfer protocol.

What would a spam-resistant successor to today's email protocols look like? Is such a thing in the works by someone?

This is completely off topic from this thread, but one way to easily cut down on spam (that would break many email senders today) would be to require that a mail server can only send email for a domain you own. Yes, I'm familiar with DKIM and similar tools, but they don't go far enough.

Another way is to accept emails only from your contact list.