Generally speaking, your email privacy is safe with Gmail and Yahoo! Mail. Unless you send undesirable emails and the government gets involved, then Google and Yahoo will comply with all lawful requests for information with proper process.
Here’s a recent case:
The US National Association for the Advancement of Colored People (NAACP) received a threatening e-mail on 22 May 2006 and notified the FBI.
The FBI then requested information from Google via a federal grand jury subpoena to release the records of the incident including the offending email, registration information, session timestamps, and originating IP addresses for *[removed]@gmail.com. Google also informed the FBI that the user applied for the Gmail account using the name “*[removed]” and gave a secondary email account as *[removed]@yahoo.com.
After examining the registration records from Yahoo, the FBI confirmed that the owner of both accounts was *[removed], a resident in the New York state. With the IP addresses and timestamps from Google and Yahoo, the FBI further confirmed that both accounts were accessed on the same day and at the same location: a law office in Weston, West Virginia.
The FBI learned that the law office maintained an annex office across the parking lot which had a computer that was not password-protected and had Internet access. That office was accessible via an adjacent apartment which *[name] rented from 20 May 2006 to June 2006. Also, he left a forwarding address as Dover, Delaware, and the FBI caught up with him there.
He admitted to accessing *[removed]@yahoo.com.
Bottomline 1: One must not send undesirable emails, coz one will never know who might be knocking on one’s door.
Bottomline 2: There’s no such thing as email privacy.
Do you send emails with private and sensitive content? How do you protect your emails’ privacy? Anyone sending encrypted emails?
* Updated: real email addresses and name removed. At this point, while he has been investigated by the FBI, no charges have been pressed against him.