1) Abbreviation before a colon 2) Abbreviation on a memo 3) Abbreviation on an envelope 4) Abbreviation on an order 5) Abbreviation on envelopes 6) Address label letters 7) Alerting word on a letter 8) Business envelope letters 9) Business envelope marking 10) Business letter letters 11) Business-envelope letters Found on https://www.crosswordclues.com/clue/attn