Rara sis Boomba

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Across
  1. 3. You send this in the post (I barely know her)
  2. 4. The start of this sentence
  3. 7. In the process of killing someone
Down
  1. 1. Six places after first
  2. 2. An organisation of letters
  3. 5. Not mine, but… (-s)
  4. 6. Opposite of out
  5. 8. Two letter word that is within this sentence