Federal law governs who has the authority to read a person’s mail or e-mail. As to mail (“snail mail”), the person to whom the correspondence is addressed has a right of privacy to that mail. A person who opens another person’s mail without permission commits a federal criminal offense.
Similarly, with e-mail, a person has an expectation of privacy in their electronic communication. If the spouse has shared the password to the e-mail, then they have consented to the other spouse reading the mail. However, guessing at the password or using other methods of reading the e-mail without the spouse’s consent is a federal criminal offense. Spouses are getting prosecuted around the state of Texas and the U.S. for violating these laws – called the Federal Wiretapping Statutes.
So, tread very carefully in reading a spouse’s mail or e-mail, especially if the marriage appears to be headed for divorce court.