The US data replicas will be resilient, and when the FBI asks your data to reveal things about itself, your data will refuse to reveal anything about itself in the characteristic resilient manner. That's why the mention of "resilient".

How is that possible if the OS/drive/vault is backdoored? Could you elaborate?

I think "resilient" just means "backup copy" and I do think (IANAL) it is illegal to destroy emails when asked for them in the US.

Or was your comment ironic? Sorry, German, irony impaired.