I often assume this kind of thing is part of an effort to filter for idiots

If you know that’s an invalid IP address, you’re probably less likely to fall for the scam after the scammer has put the setup work in. So if they filter you out before a scammer has to spend any actual effort on you, that means more time they can spend scamming people who might be more likely to fall for it

That’s why these things often have egregious spelling errors and other seemingly obvious red flags

It’s possible in general, but I don’t think that’s what’s going on specifically here; not many people read IP addresses in such detail to notice such things at first glance.

It’s exactly what is happening, they’re filtering out people who know what an IP address is and can contain so that they get fewer time wasters.

The point schnurrito was making is that even if you know what an IP address is and what are valid or invalid IP addresses, a lot of people won’t read the IP address. They’ll just see numbers and skim over them. Even if you’re keeping eyes peeled for scams, most people don’t have their IP address memorised off the top of their heads so they wouldn’t be looking to check if the IP address looks right or not.

And the point I’m making is that they’re doing it to filter out people who know and pay attention. Real simple stuff.

Then I don’t think that would be the most effective way because most people aren’t paying that much attention, independently of knowledge. What would tip me off to it being a scam would be other parts of the email.