Crossword Puzzle Post office objective?

Clue: Post office objective?

Cry at the post office (NEXT with 4 letters)
Did post office work (SORTED with 6 letters)
Post Office purchase (e.g. BOXNUMBER with 9 letters)
Former Post Office service (SPECIALDELIVERY with 15 letters)
Post office needs (FLAGS with 5 letters)
Special-handling designation at the post office (REGISTEREDMAIL with 14 letters)
Drops in a post office slot (MAILS with 5 letters)
Post office unit (OUNCE with 5 letters)
Post office need (e.g. DATER with 5 letters)
Post office? (STAMPINGGROUNDS with 15 letters)