Free relays is a paradise for the spammers make it paid! That way you have more decent users increase your privacy and get paid for your work, time spent and costs.
Discussion
Or PoW is another option 🤷
mobile users wouldn’t even be able to use it then, like Damus doesn’t do POW
Well PoW is well documented but i never saw that config in any relay do you?
nostr:npub1y757ulku2jrgstt6e4s7vccl7x9qn6vmdmj7gkgx78gdccxxra0swmydh8 might know to answer this. I don't have a lot of knowledge how things work under the hood.