@Someone:
Encrypted mail could be useful in a bunch of different (
legitimate) situations (and some of those are not even that
special):
1. Business secrets (communication that contains proprietary information). The type of information can range from some know-how to some business decisions (e.g. trading, market expansion, etc.).
As you probably know, industrial spying could be more fierce than state spying.
2. State, military, secrets.
3. Variety of client-service_provider communications where privacy is at stake, e.g. client-attorney, patient-doctor....
4. Personal communication (between family members or with romantic partners).
5. Communication of private information (e.g. Social Security Number, credit card numbers, etc.)
6. Other, semi-private business communication.
There are also many other situations, some of which are somewhat extreme, and as such is not related to a "mass market" use case (such as communication of whistle-blowers with journalists, communication of political opposition, etc.).
Of course, for #2 above, and even #1, people should not traditional e-mail system and Android devices.
Even though it may look encrypted e-mail communication is needed only for very small portion of users, the situation in #5 above affects many people. And some people have to invent workarounds (e.g. password-encrypted .zip files), many others are foolish enough to send information in the clear.
I think the reason the encrypted communication has never became "mainstream" is the complexity of its setup. I might be in the dark on this, but I am not aware of any e-mail client (or webmail provider) that makes it easy for non-technically-savvy people to set up and use encrypted e-mails. And the fact that the majority of the users do not recognize the need for the encrypted e-mail, contributes to the lack of the "critical mass" of users.
For an example of how such capability can be enabled, say, in Thunderbird, you can read this page:
http://wefightcensorship.org/article/sending-encrypted-emails-using-thunderbird-and-pgphtml.htmlOnce it is properly installed, it is fairly easy to use it (assuming that your correspondent also has that capability enabled).
I don't think I've ever used an encrypted e-mail myself. However, I've relied on another capability of essentially the same software: digital signing of e-mails.
This is a bit more frequent functionality that is used. E.g. all security announces from FreeBSD team are digitally signed, so that you can verify authenticity of those.
I hope this addresses your curiosity.
