> "Often" but as a tiny fraction of all sender cases

Not really, no. I mentioned and you're dismissing high-rate legitimate senders and low-rate spammers. The former happens for example when companies send bills each month, they hit very high rates compared to their usual baseline. The latter is not the majority volume-wise, but is the most annoying - fairly logical that some spammers choose to fly under the radar and drop a letter or two in a minute. Do that during the night and you've landed a lot of letters in people's inboxes before you get reported.

> And, the vast majority of individuals do not send high volumes of email. This is a fact. It is an edge case.

It may be an edge case for you, but it must be accounted for. You can't wave it away because then people won't receive their mail. Just one minor example, some less tech-savy users emulate mailing lists with hundreds of people in CC. You can't say there that "oh this is my anti-spam solution but it doesn't account for you because you're an edge case"

> Also, low-volume spammers are quite clearly an oxymoron - the definition of "spam" includes high volume.

There's a difference between total volume and rate. You confusing the two is your problem. Not to mention that a dictionary definition is not the ground truth neither does it define "high volume". I'd also say unwanted unsolicited advertisement sent to 30 people is still spam, but you do you.

> You seem to be making a lot of arguments from authority, yet you don't even have the credentials to back them up.

From experience backed up with explanations, and you're dismissing them based on yours with no explanation.

> Literally no anti-spam situation protects against this, so it's irrelevant, and I don't know why you're bringing it up.

Incorrect. Looking at IP addresses suddenly behaving unusual is a great signal compared to the aggregate of a domain's total.

> Then these need to be fixed. Google indiscriminately blocking smaller senders isn't a fix.

They absolutely should be, but it's difficult and in the end you're not alone on the internet. Until people will, IP's continue to be used for spam classification.

And no, it's not indiscriminate.

> Exactly - that's what Hashcash does [...]

I think you misunderstood again and let me rephrase. Spammers spend more effort to lower effort spent per unit of spam. So in the end they spend less effort per letter than legitimate small senders.

> This conclusively illustrates that you have no idea what you're talking about. Spammers do not get resources for free

Your sentence conclusively illustrates you're clutching at straws. Declaring that something stolen hasn't been gotten for free is a shaky foundation to build your argument upon and pedantry at worst. The cost to acquire those resources is there anyways, some extra CPU they have to steal is not that significant.

> Hashcash directly increases the cost of spending spam email by making it compute-bound on top of needing to acquire domains, IP addresses, and machines.
> Normal users don't have to do that again because they don't regularly burn their acquired reputation.

You're going in a loop again. We're comparing relative effort/monetary cost per email here. If one side has lowered the cost of effort by parallelizing things it's unfair to the side that hasn't. Consider the scenario where a new online store owner starts sending email or someone's script is compromising yet another poorly secured blog, IoT device or SMTP account.

Now a legitimate sender has built up all the reputation, after a few flags by recipients it was spent in an instant. Everything will become slow and expensive for the actual owner, once again. For spammers it was the tenth one that day.

Such a massive extra cost for the spammers. /s

That was just one example. Again it all boils down to the fact that regular users can't parallelize their actions in the same way spammers can - PoW would make it *relatively* more expensive (time+effort+money) to legitimate users per email.

> The fact that you can't actually counter these arguments about Hashcash sounds almost like a spammer who's worried about the deployment of an effective system based on Hashcash.

So many ad hominems, so little substance.