You might not know this about Hushmail, but I'm supposing that you might want to:
Message headers are NOT encrypted on their servers.
What are message headers? Nothing important: Sender, Receiver, Subject line, Date, ...
The right message headers --> justification for "further activity" by LE.
Check for yourself
"Message headers in storage on web server: Not encrypted"
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Encrypted mails might have the body text of your messages encrypted and offshore, unable to be pulled up on demand, BUT quite a lot can be found out without seeing the body text of all of your messages.
Take care.