For a long time now, I’ve used Gmail because of how convenient it is. From a security perspective, Google encrypts all the traffic between your computer and their servers using HTTPS, however if you send an email to a non-Gmail user, your email is sent in plain text to the other email server. This makes your emails easily intercept-able and readable by the NSA and any other organization that has control of a router between Google and the other email provider. This is why the US general Petraeus who used to be in charge of the CIA used a single Gmail account as a “drop box” to communicate with his mistress via email drafts rather than send emails or text messages to her; because he knew that email traveling between service providers is intercepted by the NSA.
If you’d like to ensure that the NSA does not get a copy of your email conversations, you can install an OpenPGP client for your email program so that you can encrypt your emails. I use a Chrome plugin called Mailvelope to encrypt my Gmail messages. If you’d like know in detail how OpenPGP works, check out this Wikipedia article on OpenPGP. Here are some OpenPGP clients for other major email clients:
Install on of the GNU Privacy Guard clients above, and then import my public key. Search for it using the short ID 735FA3DA or download and import my public key from Google Drive. I create new keys regularly so be sure to use this key and not older versions. You can also copy and paste my public key from the text block below. Good Luck!