Sorry, but I'll decline to do your research and note this one has been regarded well. If you are expecting a full report, I must decline.
However most of these have WIKIPEDIA entries for your reading please such as http://en.wikipedia.org/wiki/Hushmail
If your clients are up to no good then these will not keep it a secret.
My boss is communicating with a client who distrusts his IT department. So this client has asked my boss what he should use to keep his messages private and of course this task has moved on to me. I did some research and found the following:
I'm trying to figure out what the differences are and which one would be best for him. Can anyone help?