This is more a sign of the sluggishness of the legal system to follow the reality. More people use email now than regular mail, even for official things. Most companies even accept a pdf of a signed contract as an attachment these days.

The thing is though, if email was treated in a way similar to Federal mail, the whole debate about encryption and due process could be handled by laws that already protect privacy. For some strange reason, because it uses a computer, we lose many fundmental rights that we already had with Federal mail. In a certain way email is a service so fundamental to society now, that it becomes a necessary utility - so many things can't be done without an email address today.