Crossword Puzzle Part of the MLB post-season

Clue: Part of the MLB post-season

Post office activity, or a hint to this puzzle's theme (LETTERSORTING with 13 letters)
Post-intermission part (ACTTWO with 6 letters)
Lines at the Post Office (ADDRESS with 7 letters)
Post-office stamp (AIRMAIL with 7 letters)
THEATER PART (e.g. AISLE with 5 letters)
Theatre part (e.g. AISLE with 5 letters)
Post-office alert letters (AKA with 3 letters)
Post office poster letters (AKA with 3 letters)
Part of the MLB postseason (ALCS with 4 letters)
Part of baseball's postseason: Abbr. (ALCS with 4 letters)