You can still analyze that Bob emailed Cindy and that Cindy emailed Marge, even without knowing the content of the emails. IIRC, the FBI has some sort of software that does this with telephone communications to identify 'networks' that was originally developed to combat the mafia.
Yes, and you can break Bob and Cindy's fingers to get their passphrases. That is a very easy step. That is why steganography should be used. There shouldn't even be an ecrypted text for them to try to decrypt, at least as far as they know. Because once, there is, they can always get the password. The next best thing is is fake encryption or some kind of nested encryption, so that the outer layer decrypts to something plausable but ultimately benign.
A password doesn't even fall under 'free speech', so even in a free country like US one can get slapped with 'obstruction of justice' if one doesn't provide a password. I'll leave it to your imagination to what happens in other, more oppressive countries...
But I guess that large webmail providers can band together and ensure that e-mails between their systems are encrypted (i.e. all messages sent by gmail to other gmail addresses or hotmail addresses are encrypted).
Then users would just use HTTPS to check their mail and everything would be encrypted.
This is not perfect, but it is at least a stopgap.
