In their online Transparency Report, Google made it abundantly clear which email providers support encryption, and which do not. They based this on the 425 million active Gmail users and found about half of email traffic is not private. The Transparency Report allows users to search by region to find out if their email provider is using encryption.
Encryption is basically an encoded message, meaning no one can read it except the sender and the recipient. Think of encrypted email as sending a locked box, where only the sender and receiver have the key. In unencrypted emails, others have the key too. Unencrypted emails mean people can snoop your inbox, and considering how privacy obsessed we are becoming, that is extremely undesirable.
For encryption to work as intended and protect your digital activity, both the recipient and sender much have the encryption protocol, called Transport Layer Security (TLS). If you are using Gmail, which is encrypted, but emailing a non-encrypted email provider, the entire email chain becomes unencrypted. The new End-to-End plug-in will change that, by encrypting it the entire way, no matter who you are emailing with.
The plug-in isn't available yet, it still has to pass through some testing and get feedback from the e-security community. Once it gets the seal of approval, it'll be available to all Chrome users, presumably for free. Google said of the plug in, "We recognize that this sort of encryption will probably only be used for very sensitive messages or by those who need added protection. But we hope that the End-to-End extension will make it quicker and easier for people to get that extra layer of security should they need it."
This is also a major stance for Google to take because it means they are willing to cut into their ad profits for the sake of security. Google makes money by scanning unencrypted emails and targeting ads based on keywords. Things like "shoe shopping" plans with a friend can lead to Zappos advertisements on your Gmail homepage. This would eliminate that ability (for encrypted emails), but Google certainly is profitable enough to take the relatively minor hit.
Slowly, but surely, more digital activity is becoming encrypted. According to Google's report, AOL, Yahoo, Facebook, Twitter, and LinkedIn encrypt about 95 percent of their email traffic. By comparison, Microsoft Outlook email is only about 50 percent encrypted, but they are looking to improve that.