On February 15th, newly-created Fediverse accounts started posting spam messages from various instances, sending invites to a Discord server for a Japanese troll organization. This spam was widespread across the Fediverse. The posts frame ap12 from “KuronekoServer” as the culprit behind the operation.
Looking at their spam content (in Japanese)
This is how email servers have worked for decades - there is no silver bullet and this comes closest. If you poorly admin your email instance, say allowing it to be an open relay (same as just allowing open registrations), you get blacklisted everywhere aka defederated. Same if you have a compromise and someone starts spamming out.