Please pray to God that this kind of work isn't suitable for you, for your Faith at all. It gives you lots of temptations and you are failed sometimes. Ask the Lord to lead you to some other jobs that He sees it's better for you, and more than that it helps you draw closer to God. Asks for His guidance Darrin.
I'll pray for you too, for He guides you to a better job and good for your Faith.
I find time in a daily chapel or adoration helps keep the lower nature at bay. How about even praying for the woman in those pics?
I was a mail carrier myself for a few months, and while I was lucky enough to rarely have to deal with explicit material, I can understand how hard it must be. Maybe you can just remember a good rule of thumb in general for a carrier: you just deliver the mail, you don't really care what it is (unless it's a dangerous package) and you shouldn't try to look at it too closely to see where it's from. I know that's tough when they put the address label on the front cover instead of the back cover of the magazine, but I would say do your best to just focus on the job you have to do and perhaps just offer a short prayer for yourself and the people you are delivering the material to while out on the route. Keep your mind occupied with other things and that should help relieve the urges. It's helped me in the past in other situations. A distraction from the distractions, you could say.
I can't believe these magazines (especially playboy and such) are not mailed in envelopes so no one can see them. When I was a teenager, we lived in a private house with an unlocked mailbox and I checked the mail when I came home from school. I'm sure there are youngsters who check the mail also and/or some of these magazines are getting into hands of children.