Even if you delete an e-mail the moment you read it on your computer or mobile phone, that doesn’t necessarily erase the content. There’s still a copy of it somewhere. Web mail is cloud based, so in order to be able to access it from any device anywhere, at any time, there have to be redundant copies. If you use Gmail, for example, a copy of every e-mail sent and received through your Gmail account is retained on various servers worldwide at Google. This is also true if you use e-mail systems provided by Yahoo, Apple, AT&T, Comcast, Microsoft, or even your workplace. Any e-mails you send can also be inspected, at any time, by the hosting company. Allegedly this is to filter out malware, but the reality is that third parties can and do access our e-mails for other, more sinister and self-serving, reasons.