So since in the USA they enjoy spying on communications from all over the world with programs like PRISM or other devilries, in case you don't want to risk that a private message is read by strangers you can encrypt it. Who uses Gmail can take advantage of the application for Google Chrome Secure GMail which is used to encrypt a message and to de-encrypt it on the computer of the recipient, so that there is no possibility for Google or others to be able to read the contents of the email, even if it were intercepted.
UPDATE: Now you can send protected emails in Gmail with expiration and password
The Secure Gmail extension works, for now, only for Google Chrome (for other browsers and other mail services, however, there are numerous different solutions).
This means that those who receive the encrypted message, to read it, will have to use Chrome, use Gmail and install the extension.
After adding it to Chrome, open Gmail to notice the appearance of a new lock icon next to the "Write" button.
Press the padlock to write an encrypted message.
The writing window has the word Secured on the title and the Enter button is replaced with the Send Encrypted button.
By pressing this button, after writing the email and indicating the recipient, you can write a password which will then be requested from the recipient in order to open the email in clear text.
You can also add a plaintext recognition word, which can serve the recipient to understand what password it is.
Note that the email has the subject (the title of the Mail) in clear text and the content is illegible without a password.
To decrypt the email, in addition to the password, you need to open Gmail with Chrome and the Secure Gmail extension installed.
If the extension is not installed or if you use another browser or another mail service, the link to download the extension is indicated.
However, the recipient cannot reply leaving the same encryption (conversations are not supported for now) and, if necessary, will have to write a new Email and password protect it.
A Chrome extension very similar to Safe Gmail is MyMail Crypr for Gmail which works very similarly.
If you use another email service such as Hotmail, Yahoo Mail or others there are other ways to encrypt an Email in order to keep it confidential.
A simple one is the InfoEncrypt site.
Write the message in the box, indicate the password and press the Encrypt button to protect it.
The recipient, who must know the password, will be sent the covered content via Email which can be de-encrypted by copying it on the Infocrypt box, indicating the password used and pressing the Decrypt key.
A site like this is SafeMess .
SafeMess allows you to indicate a password also generated randomly and to write a message that is protected.
You can also choose an expiration time so that the encrypted message is destroyed after a certain period of time has passed.
This means that if you protect a message by setting self-destruction in 24 hours, those who have the password after a week will still not be able to read it.
One of the best Chrome plugins to encrypt mail sent with Gmail, Yahoo and Outlook.com and which can also work with other email providers is Mailvelope, a little less simple to use, but still extremely flexible.
With Mailvelope you need to create an encryption profile which will then be used for all accounts opened with Google Chrome.
The keys are stored only locally in the browser and are sent to the recipient.
Finally, another article lists the best e-mail providers to send password-protected encrypted emails
