E-mail Privacy
When you use e-mail, especially a "free" e-mail service, as well as using Google, Facebook, and other free social sites, you are trading your data for the convenience of using that product. The same with free file-sharing sites.
Even using a paid e-mail service, when you delete a message it's not really deleted; it still exists somewhere. Most companies keep archival data to protect themselves.
When someone calls the FBI to investigate messages you sent, and then the FBI reads the message to determine just cause, and then opens an investigation, they then obtain a legal warrant to search your e-mail history.
There is no privacy on the Intenet; only secrecy.