Something that becomes very apparent about The Postman quite quickly is that its editing is a bit of a jumble. Early on there's a scene of the Postman in a ransacked store, and then suddenly he's in a town performing Shakespeare for kids. I thought "oh, this must be a pre-apocalypse flashback" since he'd had a couple quick flashbacks already... but no, a couple minutes later the party gets interrupted by a bunch of raiders and it becomes clear that this is in the present. Well then, that raises more questions... like where did his gun go? How did he find the town? Honestly, moments like this happen throughout the entire movie.
Even worse, the entire opening 50 minutes of the film are completely unnecessary. The film seems to be setting up something important, but it literally all gets thrown away all of a sudden... even all the secondary characters and one of the villains get killed too. To make matters worse, this ruins any sort of mystery that they could have derived from the premise. How much more interesting would it be if we were wondering if The Postman was telling the truth or not? If they played with our own sense of optimism for the reestablished US Government then it would be far more interesting than a completely unnecessary opening act that spells out everything for us.
My main issue with the opening however, is that it adds 50 minutes to an already overlong film. People bitch that The Hobbit is overlong. While they are right about that it doesn't feel unnecessarily so (well, most of the time anyway). However, The Postman has no excuse to be a 3 hour "epic" whatsoever, and could do with some serious trimming of the fat. As it is, the film is excessive, bloated and boring half the time - cutting out the opening would have made it a hell of a lot more bearable.