Crossword Puzzle Post office issues

Clue: Post office issues

Some post office machines (SORTERS with 7 letters)
Letters from the post office? (COD with 3 letters)
Post-office fixture (FLAGPOLE with 8 letters)
Drops in a post office slot (MAILS with 5 letters)
Mil. post office (APO with 3 letters)
Post office gizmo (DATER with 5 letters)
Post office department (GENERALDELIVERY with 15 letters)
Post-office device (SCALE with 5 letters)
Post office scale unit (OUNCE with 5 letters)
Post office activity, or a hint to this puzzle's theme (LETTERSORTING with 13 letters)