Why has e-mail taken the world by storm?

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Across
  1. 2. to erase
  2. 3. interaction with another person such as speaking
  3. 6. joined with another person for life
  4. 7. to burst or to break apart
Down
  1. 1. a person you do not know
  2. 4. a single person
  3. 5. an extreme weather event such as a typhoon