Creating an account in Scramble.io only requires you to choose a username and passphrase, your personal OpenPGP keys will be created in the browser during sign up, if you forget your passphrase it can’t be reset and your emails will be lost for ever. To distribute your public encryption key to friends you can copy and paste it by going to the Contacts tab in the interface, or upload it to a public keyserver, in the same tab you can access your private encryption key.
All email messages sent to other Scramble.io addresses are automatically encrypted and verified, if you email someone at Yahoo or Gmail encryption will only be done automatically if you have previously uploaded their public encryption key to Scramble.io. If you haven’t got the encryption keys for the person you are emaling to, a warning window will pop up telling you that the message is being sent unencrypted. Scramble.io can’t do magic, you need to get your friends to create an PGP key for communications to be secure, either that or you both use the same secure email provider.
While Scramble email interface is really basic and not able to send attachments, it does the job and it has shortcuts. This not a webmail provider that can compete in features with others, but it has good security. I checked the email headers sending myself a test message and Scramble.io will not show your computer IP when sending email, it is replaced by an IP from a US data centre (Linode).
The datacenter , although not being able to read the emails, could monitor who is communicating with whom but this is not something the NSA needs. OpenPGP can not scrub metadata, the to and from fields are not encrypted and the wire-tapping that the NSA has on deep sea Internet cables will know who is emailing who, frequency and size of email, regardless of if the server is in the USA or China.
The best part of Scramble.io is that it is an open source project and anybody can set up their own Scramble encryption email server. Note that this is a prototype and work in progress.