@mapto No, I do not start with an invitation to defederate! I start with an invitation to mute. Any instance can set the status of any other instance - muting on Mastodon is like a soft defederation. Your users will not get any spam or any messages from this other server, however the people they're following remain as followers and the people who follow them too. So nothing is permanently broken like with a defederation, but you will still stop having spam.
@ErikUden apparently I'm having difficulties with reading the text of you post. On my device it appears to read "defederate". Anyway, thanks for clarifying that you mean "mute"