Is It Legal to Publish Email Correspondence Without Permission?

From the Mueller investigation to Donald Jr.'s alleged contact with Russians to the Stormy Daniels fiasco, the Donald Trump administration is demonstrating how powerful emails can be when made public. Thus far, no one has gotten into any legal trouble for acquiring or leaking those emails, though they've certainly gotten the president in some hot water.
Chances are, you don't have such incriminating emails sitting in your inbox, but could you get in trouble for "leaking" them anyway? Can you publish someone's emails to you without consent? It largely depends on the content of the emails and your purpose in publication.
Content
Depending on the information contained within the email, there are various ways you might get in trouble for publishing its contents:
National Security
There are a slew of federal statutes that make it illegal to disclose national defense information, government secrets, classified information, or the identity of government agents without authorization and to someone not entitled to receive it. Oh, and it's illegal to lie to the federal government about it. Then again, most of us aren't getting those emails in the first place, so you're probably OK on the state secrets front.
Confidential Information
We've all seen the long, sometimes in italics, sometimes in all caps disclaimers at the bottom of work emails, warning us that the email contains confidential information, and disclosing such information will lead to your legal and professional downfall. While some of these disclaimers may be unenforceable, if you've signed a non-disclosure agreement or you're dealing with particularly sensitive corporate data, your bosses will probably be coming after you.
There are some so-called "whistleblower" protections that can shield people who release government or business information related to illegal or unethical practices, but those protections can be limited and hard to come by.
Private Facts
Even if you're just dealing with personal email correspondence between friends, there are some disclosures that can still get you into legal trouble. There is a cause of action, known as the public disclosure of private facts, which allows someone to sue if a disclosed fact was private (not publicly available), was publicly disclosed (or to enough people that it's reasonably likely to become public knowledge), and the disclosure would be offensive to a reasonable person of ordinary sensibilities. Just something to think about before posting your ex's emails to social media.
Copyright Information
Finally, some information contained in emails may be subject to copyright protection. If the contents are an original work, including literary works, photographs, movies, or software, you may need authorization to publish it publicly, whether or not it's already been published.
Purpose
Your motives may come into play when determining whether publishing email correspondence will be legal or not. As mentioned above, whistleblower laws may protect you if your intent was to shine a light on illegal behavior. On the other hand, many states are enacting revenge porn laws that could apply to illicit images received via email. And if you're lifting conversations to use for a publication like a book or memoir for sale, you're more likely to run into copyright concerns.
Publishing private correspondence can obviously be legally complicated, so before you make emails public, talk to an experienced attorney first.
Related Resources:
- Find Your Lawyer (FindLaw's Lawyer Directory)
- Legal How-To: Using Email as Evidence (FindLaw's Law and Daily Life)
- Will the Email Privacy Act Become Law? (FindLaw's Law and Daily Life)
- Is It Legal to Spy on Your Spouse's Email? (FindLaw's Law and Daily Life)