"Before Sending" is the lynchpin here.
The receiver needs to be performing verification, and have the ability to blacklist sources.
Which requires distributed infra.
I had a go at trying to sketch out a protocol for this years ago, that was low enough level to be actually mildly censorship resistant and also pay out for middle men successfully routing traffic and there was something like 10-100 times more protocol traffic on network than actual packets. It was a mess.