The recipient doesn't own the material and is limited when it comes to publishing it.
The folks who sent death threats to Sarah have a problem though ~ their communication was UNLAWFUL so they don't get to assert a right to restrict the message.
That's another reason to always be polite. As long as you project a pleasant demeanor no one will challenge your implicit right of ownership of your own messages.
If the authors of the emails have any complaint it would be against the judge who ordered the disclosure of the emails.