The Post Office, and others, have made occasional noise (none of which I take seriously, yet) about taxing emails as a way to make up for lost postage revenue. But in my personal experience, the only thing I used the post for was mailling bills. The advent of online banking, with automatic bill pay, means that I practically never send regular mail. I had to mail my car tax today, and I couldn't even remember what the postage rate was. The stamps I had on-hand were $0.34 from back in the spring (a sheet of 25, of which I have probably 15 left).
I'm pretty sure letter writing was already a lost art by the time I was growing up, but the real hurt is going to come when commercial mailling goes the way of the dodo. I already throw away 80% of my mail in the post office because it's spam. (I got five credit card offers from CitiBank in a four week period, for example.)
I guess it just goes to show that if there's an activity going on, the government will want to regulate it or tax it.