Spam is a challenge for Nostr. Anyone can create a keypair and anyone can post. Low barrier to entry means spammers can create endless accounts.

Defenses exist. Proof of work raises the cost of bulk posting. Paid relays filter out casual spam. Web of trust can prioritize content from people your follows follow. Clients can implement spam filters, with some hiding posts from accounts with no followers and some using reputation systems.

No solution is perfect, and spam is an ongoing arms race. But the decentralized architecture means different relays can try different approaches, and what works will spread. Your personal defense: mute aggressively and use relays with good policies.