I don't think even what you said is sufficient -- as long as they are within the jurisdiction of the US court system, I think a judge can order them to start sa

I don't think even what you said is sufficient -- as long as they are within the jurisdiction of the US court system, I think a judge can order them to start saving copies of incoming mail before encrypting, etc. I think fundamentally you can't circumvent the law with technical measures. You need to change the law to require warrants.