Postmark Ganymede

Consider the poor mailman of the future. To sleet and snow and dead of night —things that must not keep him from his appointed rounds—will be added, sub-zero void, meteors, and planets that won't stay put. Maybe he'll decide that for six cents an ounce it just ain't worth it.
I'm washed up, Preston growled bitterly. They made a postman out of me. Me—a postman!
He crumpled the assignment memo into a small, hard ball and hurled it at the bristly image of himself in the bar mirror. He hadn't shaved in three days—which was how long it had been since he had been notified of his removal from Space Patrol Service and his transfer to Postal Delivery.
Suddenly, Preston felt a hand on his shoulder. He looked up and saw a man in the trim gray of a Patrolman's uniform.
What do you want, Dawes?
Chief's been looking for you, Preston. It's time for you to get going on your run.
Preston scowled. Time to go deliver the mail, eh? He spat. Don't they have anything better to do with good spacemen than make letter carriers out of them?
The other man shook his head. You won't get anywhere grousing about it, Preston. Your papers don't specify which branch you're assigned to, and if they want to make you carry the mail—that's it. His voice became suddenly gentle. Come on, Pres. One last drink, and then let's go. You don't want to spoil a good record, do you?
No, Preston said reflectively. He gulped his drink and stood up. Okay. I'm ready. Neither snow nor rain shall stay me from my appointed rounds, or however the damned thing goes.
That's a smart attitude, Preston. Come on—I'll walk you over to Administration.
Savagely, Preston ripped away the hand that the other had put around his shoulders. I can get there myself. At least give me credit for that!
Okay, Dawes said, shrugging. Well—good luck, Preston.