No. They can install a device at your ISP to trap all your emails and send copies to them. The ISP will be ordered to keep it confidential or go to prison.
You can also put high-speed sniffers and minicomputers to route copies of all traffic over a portion of the Internet backbone and read all the email and web pages and files being transferred and pin those to IP addresses. If something is suspicious, they can get a warrant to make your ISP identify you by name/address so you can be arrested or subpoenaed or whatever.
There's the Patriot Act then. And this court is trying to clip its wings by making them get a subpoena from a judge first, like a wiretap.
Oh, and your employer has the right to read all your email too. They can dig back years and mine all those old emails for any wrongdoing. Interestingly enough, there are also laws requiring government to keep all of its old emails as well and that is part of the scandal over email from 88 officials at the White House which were posted via the RNC server to keep them out of the official record.
"These e-mail accounts were used by White House officials for official purposes, such as communicating with federal agencies about federal appointments and policies... Given the heavy reliance by White House officials on RNC e-mail accounts, the high rank of the White House officials involved, and the large quantity of missing e-mails, the potential violation of the Presidential Records Act may be extensive."Via: White House Aides' E-Mail Records Gone - washingtonpost.com