How to "Fix" the USPS

I've been hearing a lot recently about how insolvent the USPS is, and how to fix the problem. Most of these solutions have run along the usual conservative lines: slash retirement benefits!

Why isn't this a viable solution? Simply stop charging so little for corporate and junk mailing. Better for the environment - less paper waste! - and more money for the USPS.

I suspect the only reason  this wouldn't work is that congress is unduly influenced by the money and lobbyists that the junk mailers throw at them.