Mayberry may have brought up a point about the phone service, but here is why I don't think that the comparison is valid.
That same logic can be appliede to phone calls. So are they fair game as well? No expectation of privacy on the phone? Better make sure Shanny's isn't bugged...The reason that that dog won't hunt is the ephemeral nature of a phone call. This is a conversation, between two individuals, mediated by contract and controlled by utility Commisions. There is clear case law to support the prohibition of phone taps without clear court order.
E-mail is a different can of fish. It is residual in nature. Copies of the text are stored for a time on every server the e-mail touches in it journey. There are no clear laws defining the privacy, and to tell the truth, it appears that the bulk of the laws are written so that there is no privacy constraints.
All that being said, I think that everything is being listened to, and one should take that possibility very seriously.