”Server admins worked together to create ongoing lists of abandoned instances that other admins could use as a basis for a blocklist to protect their own users from the spam attacks. Many servers were simply shut off as their admins decided it would be easiest to wait out the attack or abandon Mastodon altogether.”

https://techcrunch.com/2024/02/20/spam-attack-on-twitter-x-rival-mastodon-highlights-fediverse-vulnerabilities