Emails can be introduced into court as evidence and sometimes count as legally binding documents. The IRS enjoins its employees to treat all emails as legal documents and remember that they should take care to reflect the "Service's image and take into account privacy, records management, and security factors."
In 2008, two men got into a traffic collision in New York, according to an article by Oliver Herzfeld published on the Forbes website. After some wrangling, the insurance carrier of one driver, named Gelco, agreed to a settlement offer via email to the counsel for the other party, Forcelli. A few days after the agreement was reached, a court in New York issued a summary judgment for Gelco, who then tried to overturn the $230,000 settlement his insurance company had just reached with Forcelli.
According to Herzfeld, the courts eventually found that the initial offer of a settlement was valid when the insurance company made it over the phone, and the details that were worked out via email were indeed legally binding. Gelco was compelled to honor the original terms of the settlement by a unanimous verdict at the Appellate Court of New York. The emails, the court found, constituted a contract.