Crossword Puzzle Post Office goal

Clue: Post Office goal

Letters that are not at the post office (EMAIL with 5 letters)
POST OFFICE (KISSINGGAME with 11 letters)
Post-office stamp (AIRMAIL with 7 letters)
Post-office opening (SLOT with 4 letters)
Post office needs (FLAGS with 5 letters)
Dead letter, in post office talk (NIXIE with 5 letters)
Post office employee (SORTER with 6 letters)
Post office activity, or a hint to this puzzle's theme (LETTERSORTING with 13 letters)
Object of playing post-office (LIPSERVICE with 10 letters)
COUNTERTOP ___ POST OFFICE (DOLLARSIGN with 10 letters)