As far as I know, this wouldn't be against the law in the U.S., unless (for example) you and your wife had gotten divorced, and the judge in the divorce case had specifically forbidden you to read her email, but you read it anyway, and your wife chose to bring a criminal charge against you. (But the crime would not be "чтение чужого мыла" -- it would be something more general like "contempt of court," I would guess.)
Also, if you worked at an Internet provider company and you were reading the private emails of customers, then possibly it might be a criminal matter. But it wouldn't necessarily be a Federal crime with a $250,000 fine, because that law applies to mail carried by the U.S. Post Office.
P.S. But IANAL!!