Email stored for less than 180 days requires a search warrant to access. But... email which is opened may be considered to be on the server "solely for the purpose of providing storage or computer processing services", in which case a court order (subpeona, etc) is required. Court orders are easier to get than search warrants.

See: http://en.wikipedia.org/wiki/Stored_Communications_Act

At the end of the day, if you have information that you truly want to remain private, it cannot be turned over to a third party and should remain in your home.