We'd all like to believe that our emails will stay private, but just thinking positively won't help a lot in this case. It helps to have a good understanding of just what protection you have against snooping. In this case, understanding just how much of a presumption of privacy exists with email will be a big start.
The Legalities of Privacy
Without getting into the legal side of things too much, just note that there are a few basic rules of privacy. Something is only private if you have a reasonable expectation of privacy. In practice, this means that you have to show that you had a subjective (personal) expectation of privacy while doing something, and that it was reasonable for you to hold that belief. If these can be shown, then certain rights come into play and may only be superceded through the processes set forth in the Fourth Amendment.
Note that these rights can be fairly limited, mainly for criminal activities. If there's enough evidence for a warrant, then your information is no longer “private," since the police or government will be able to access anything that's left legally. The Patriot Act threw in some interesting twists to personal privacy, and at the moment, a number of records could theoretically be pulled at any moment if it can be argued that they are vital to counterintelligence and eventually approved by the classified actions of the Foreign Intelligence Surveillance Court. While this is worrisome in a grand sense, for most people's practical communication and searches, this probably won't come into play.
Issues with Email
The biggest problem with email is there is some debate as to whether one actually has an expectation of privacy. Most people just look at email as an electronic version of mail, which is understandable, of course. The issue is that it isn't really treated in the same way as a letter.
The contents of an average letter are not read at any point in the chain. You can assume that only the receiver will see a private letter without really stretching logic. But what about emails? The average email is sent across a number of servers, scanned and effectively “read” in an electronic sense for spam and ad filtering and then delivered. Emails, therefore, are seen as a somewhat special case. A bit of a Schroedinger's cat, stuck somewhere between correspondence and data.
Emails are also stored in multiple locations. You can have a letter shredded or allow the contents of a phone call to disappear into the aether (depending on phone recording laws in your state). On the other hand, there will be copies of your emails available in your sent mail folders, the recipients' inboxes and the servers of the mail providers. The fact that they have indefinite access to this information adds in another layer. Add in the fact that most email providers and Internet service providers have terms of service that allow them to monitor your usage, and it becomes harder to argue a clear presumption of privacy with your email, at least in the same way that other communication is protected.
Because of these issues preventing a clear presumption of email privacy, special laws usually regulate it.
Laws Around Email
In the United States, the Electronic Communications Privacy Act, and the Stored Communications Privacy Act within it, states that email messages are considered private correspondence for a period of 180 days if they are unopened. A full search warrant is necessary to read the message. After 180 days, or after the message has been opened, the messages are officially treated as data and can be obtained through much more simple court actions, such as a subpoena.
Note that employers may monitor messages that go through their own networks, so emails sent for work and during work are not usually private. Privacy at work is a separate issue though, and if you'd like a closer look at that we have a separate article on the wonders of workplace privacy.
What It Means
To wrap this up, don't have a lot of faith in the privacy of your email. After six months, it's just considered text that they can ask your email provider for. While you don't realistically need to fear a 1984 state at the moment, just note that your emails can last for a while, be accessed from multiple points and ultimately don't offer a lot of protection in the long-term. There's not a good case for a presumption of privacy, at least at this moment.
If you really want to keep things private, stick to methods that don't leave as much of a paper trail. Like paper.
Please note that I am not a lawyer, nor do I claim to be. If you are in a legal dilemma, or plan on getting into one, please consult an appropriate professional.
- Image from Wikimedia Commons/Sevela.p – Issued into Public Domain
- Notes from Office of Justice Programs Page
- Text of Stored Communications Privacy Act, Cornell Law Directory