Let me share an anecdote which came to my attention a few months ago.
There are strict censorship laws in China and breaking them is to beg a harsh punishment.
One of the operating agreements between Yahoo! and China is that Yahoo! will report anybody who talks about certain things in their e-mails. This is done in exchange for Yahoo! not being blocked by the great firewall of China. A Chinese journalist shares with an American colleague contraband information via his Yahoo! e-mail account. Yahoo! tells the Chinese government and the Chinese government arrests the Chinese journalist.
This highlights something many people don’t realize. That sending an e-mail is analogous to sending a postcard. Anybody who handles it along the way can take a peek.
With today’s political climate and reports of the NSAs recent activities it is more important than ever to start putting e-mail into envelopes of encryption.