Using NeoMailbox gives me peace of mind
This is essentially what I'm talking about. It probably shouldn't give you peace of mind. You click an 'Encrypt' button on a web interface and it encrypts it and sends it off. I presume that you can go into your 'Sent Items' and look at that email's contents even though you've encrypted it, yes? So it's either sitting there unencrypted on the server or they have the keys.