From the article:
There are those that claim encryption is dead. Not so, says many small and medium sized businesses across the globe. There are plenty of reasons why you might need to encrypt an outgoing email – just as many reasons as there are ways.
Mailvelope is an extension for Chrome and Firefox that seamlessly integrates with Gmail, Yahoo Mail, Outlook.com, and GMX. With Mailvelope you can generate the necessary keys (which are stored on your local machine) and import other users keys. This extension works from within your web-mail client when you go to compose an email.