title: Google Spreadsheets. Extract a list of email addresses that are in a sheet
body: <p>In Google Spreadsheets. I have a large sheet containing lots of bookings, a booking has several columns for name, voucher number, email address etc.  Each date I have a class on covers several columns and rows.   I want to build a single vertical list of every email address in the sheet.  The email addresses are in different columns and different rows.  I was thinking FILTER or LOOKUP but I can't quite find the answer that works.    </p>
  
  <pre><code>Dec 17th 2-5            
  Name    Voucher Email           People  
  Richa   yes     richa@xx.ca     2  
  Jessica yes     jess@sss.com    3  
  Beth    cash    ebeth@hh.com    2  
  </code></pre>