Whiteout.io HTML5 mail App with integrated OpenPGP encryption from Munich, Germany. Usable as a chrome extension, mobile phone app or self-hosted (Node.js). They also offer free and paid managed mailboxed. The code has undergone a full security audit of their sourcecode by Cure53.
Keys can easily be generated (2048 bit) on the client, imported, exported and revoked. Users have the option to use a encrypted private key sync if they conveniently want to use the same key on multiple devices. Whiteout will transparently search for public keys of peers by querying common public key servers. Sent encrypted mails are encrypted to self before they get saved to
Whiteout can handly one one mail account at a time. Extended features like signatures are also currently not supported.
The company behind Whiteout also offers a paid and a free email service. They claim to save all emails encrypted using the users privately held key. That means Email (after beeing received and temporarily stored unencrypted at Whitout servers) would need to go to a client to be encrypted with the private key there and then sendt back to server to be permanently stored.
In Mailout we find two interessting concepts: For one the ability to pre-encrypt data before sending it out. And for the other that this functionality requires no software installation process.