It's not easy. For one, we know from documents released by Edward Snowden that the NSA can — not necessarily does, just can — surveil massive amounts of electronic communication, storing what it finds in an extensive database for later analysis.
However, there is a limit to what the NSA can do: if your communications are encrypted with a strong enough password (at least 20 random characters) and the NSA intercepts your message, all they'll see is encoded gibberish.
So how do you encrypt your email? Turns out, it's not easy. Lavabit, a free service that used to offer end-to-end encrypted email, has shut down, and Silent Circle, which offers a suite of encrypted communication apps, recently closed down its secure email service.
That leaves you wading through the confusing, poorly documented tangle of open-source programs and software projects.
Finding the right encryption program
Finding an up-to-date program that uses proven encryption algorithms is the easiest part. Then you need to find something that works with your computer setup — something compatible with your operating system, desktop email clients and email service.
If you type all these criteria into Google — "Gmail Chrome encryption," for example — you'll find several Chrome apps to choose from. However, most encryption programs are still difficult to use because their graphical user interfaces (GUIs) are either roughshod or nonexistent. This means users have to navigate many complicated menus or even use the command line to type instructions.
It's hard to ask an average technology user to put in that kind of effort.
"To the extent that [the security] space needs innovation, it is not in the area of cryptography, but in the area of user experience," said Moxie Marlinspike, a security and encryption expert best known for co-founding Whisper Systems, a data security company acquired by Twitter in 2011.
No more secure email accounts
Earlier this summer, Google argued in court that its millions of Gmail email users had no "objectively reasonable expectation of confidentiality," and that the company had every right to examine all correspondence that passed through its servers.
This may seem shocking, but Google is correct: Legally, it's no surprise that Gmail communications aren't necessarily private.
In the past, people who wanted guaranteed email privacy could turn to services such as Lavabit and Silent Circle. But after it was revealed that former NSA contractor Edward Snowden used Lavabit, possibly to avoid NSA detection while collecting and leaking hundreds of confidential documents, the service shut down, citing unspecified legal difficulties.
"Without congressional action or a strong judicial precedent, I would strongly recommend against anyone trusting their private data to a company with physical ties to the United States," Lavabit founder Ladar Levison posted on the now-inoperable website.
A day after Lavabit shut down, Silent Circle shut down its own encrypted email service, though its encrypted mobile apps such as Silent Phone and Silent Text are still available. Silent Circle's chief technology officer, Jon Callas, wrote that the company had decided to end its email service because it could no longer ensure its users' security.
How PGP works
You may have heard people say they use "PGP," or "Pretty Good Privacy," to encrypt their email.
The name PGP originally referred to open-source encryption software developed in 1991. PGP was so influential that its encryption method, called the "OpenPGP Standard," still forms the basis of most encryption software, apps, plugins and other services found today.
Security firm Symantec eventually bought the original software named PGP, which is now incorporated into Symantec's paid services. But when people say "PGP," they are usually referring to any kind of software that follows the OpenPGP standard.
PGP-based encryption is still popular for a number of reasons. For one, every OpenPGP user has two encryption "keys," or pieces of information that make an encryption algorithm work, similar to the way a key opens a lock.
One of these keys is public, and one is private. So if you want people to be able to send you encrypted messages, you can give them your "public key." Using this key, your correspondents can encrypt their message so that only you, using your corresponding "private key," can unlock and read the message.
The advantage of this system is that I don't have to worry about my public key falling into the wrong hands. So long as my private key is safe, I can publish my public key on a website, or email it in an unencrypted email, which makes it easy to set up a secure connection with other OpenPGP users.