Email is more or less sent in clear text for a significant portion of its journey in most cases. Sender ----> SMTP ---*unencrypted*---> SMTP ----> Recipien

Email is more or less sent in clear text for a significant portion of its journey in most cases. Sender ----> SMTP ---*unencrypted*---> SMTP ----> Recipient I'm leaving out a lot of transport detail for brevity, but that's the essence. Also, email is generally stored unencrypted at rest. Even if you take precautions to secure your own mailbox, the recipient might just have it floating around in plain text in their Gmail account, just waiting for it to be nabbed by whoever can get a court order, or whatever. Also, even if your email is encrypted, the metadata isn't. So you can figure out who is talking to whom, when, and usually from where (by the IP address). Also, there are a lot of headers indicating details about your computer (if you used a fat client rather than webmail), such as the user-agent header which indicates what software you're running (e.g. Thunderbird, version x, on Linux/Windows/OS X for x architecture, etc) which can give clues about how to attack that client with some 0day exploit.