Hey, from the beginning of SMTP, running an open relay was an administrative mistake. The MTA administrators were supposed to know what they were doing, because resources were allocated to them. They had privileges granted for the system and the network. It was right if they were blacklisted for misuse of those resources.

Now in 2026, running a "public proxy" doesn't take an administrator. You don't even need to be aware. Most victims are unknowing victims. They simply subscribe to an ISP and they have their own devices. They are being exploited for that innocence and ignorance. Most victims have no visibility to even detect that they're being used as a proxy. Most victims couldn't stop it, even if they wanted to.

I challenge anyone with a home router to list the processes running on that router, and list all current open connections on that router, and list all open, listening sockets on that router. I bet you can't do it. There are no consumer router OS that lend themselves to being secured, or even diagnosed. Malware can easily be planted on any of them and run, completely invisibly.

A residential proxy server could run on routers, could run on a switch, could run on your "Smart TV" or a smartphone, or a notebook computer. It could be anywhere in any form. Perhaps you consented to it, perhaps you didn't notice.

In no way is this the same as an SMTP open relay situation. If you wanna play "whack-a-mole" with a "blackhole list" you're simply going to overwhelm those lists with false positives and collateral damage. The residential proxies have long since moved on. You won't even find the culprits using those addresses you just blocked. You're just clogging up your own machines. It's a total self-own.