I was reading my favorite tech resource, Langa List, when I came across these paragraphs in a response to a question about email security:

Email almost never goes directly from sender to recipient. Instead, it’s usually stored, albeit briefly, on at least two mail servers along the way, and maybe more; and will also pass through a large number (10-30 is common) of other computers, routers, and similar hardware along the way. US courts have recently ruled that email stored on a mail server (and that includes email passing through one mail server on its way to
another, "stored" on the intermediate server for only a fraction of a second) is not protected by wiretap laws originally designed with telephone conversations in mind. This is a brand-new ruling (about a month ago), so the ripple effects are still being sorted out, but in essence, it looks as though an email communication may be legally about the same as a conversation you have on a busy street corner: You can have
no reasonable expectation of privacy, so anyone who overhears the conversation— or reads the email— isn’t breaking any law.

The original intent of this legal change was for law enforcement: Along with the provisions of the Patriot Act, the idea was to make it easier for police and government bureaucrats to look freely in places that used to require a warrant.

Regardless of how you feel about that, the unintended consequence of this may be enormous. One example: If your email no longer has any legal privacy protection, what’s to prevent an ISP from, say, selling his mail server’s backup tapes to a spammer, who could then mine the addresses *and content* for likely spam targets and topics? If your email is now no more legally protected than a conversation on a public sidewalk, I don’t know what recourse you’d have at all."

Realistically I’m less worried about the "expectation of privacy" and much more worried about "selling mail server’s backup tapes to a spammer."  Someone with a mail server looking to make some quick cash selling lists to a spammer seems much more likely, and just one more straw ready to break the back of one of the great communication tools of the modern communication tools.