Stop Facebook from Spying on You...: And Other Ways to Protect Your Online Privacy (2015)

Don’t Let the FBI Read Your E-Mail!

FBI officials can read messages that are more than six months old without a warrant.

To protect your messages: You can encrypt them before sending them if your e-mail provider allows this, but the recipient must have your encryption key to read the message.

Alternative: Delete older e-mails regularly. Or store them on your hard drive, which is protected by the Fourth Amendment (the right to avoid unreasonable search and seizure).

Also: Consider an e-mail service that uses servers based outside the US. Offshore e-mails are not subject to the same rules as ones within the US. But other countries have their own privacy rules—be sure you know them. And access through offshore servers may be slower than access through domestic e-mail providers.

Source: MarketWatch.com