Going Postal by Terry Pratchett

Moist von Lipwig was a con artist and a fraud and a man faced with a life be hanged, or put Ankh-Morpork's ailing postal service back on its feet.It was a tough decision.But he has to see that the mail gets through, come rain, hail, sleet, dogs, the Post Office Workers' Friendly and Benevolent Society, the evil chairman of the Grand Trunk Semaphore Company, and a midnight killer.Getting a date with Adora Bell Dearheart would be nice, too.Maybe it'll take a criminal to succeed where honest men have failed, or maybe it's a death sentence either way. Or perhaps there's a shot at redemption in the mad world of the mail, waiting for a man who's prepared to push the envelope...