Crossword Puzzle Scale unit at the post office

Clue: Scale unit at the post office

Post office scale unit (OUNCE with 5 letters)
Postal scale unit (OUNCE with 5 letters)
Post office unit (OUNCE with 5 letters)
Postal scale units (OUNCES with 6 letters)
Post office activity, or a hint to this puzzle's theme (LETTERSORTING with 13 letters)
Post-office unit: Abbr. (RLO with 3 letters)
Attained, as as office (ACCEDED with 7 letters)
Lines at the Post Office (ADDRESS with 7 letters)
Post-office stamp (AIRMAIL with 7 letters)
Post-office alert letters (AKA with 3 letters)