function getEmails() {
  // set spreadsheet and retrieve labels
  var ss = SpreadsheetApp.getActiveSpreadsheet();
  var labels = GmailApp.getUserLabels(), emptyLabels = [];

  // itterate through the labels
  for (var i=0; i<labels.length; i++) {

    try {
      // create sheets and clear content
      var sh = ss.getSheetByName(labels[i].getName()) ||
      ss.insertSheet(labels[i].getName(), ss.getSheets().length);
      sh.clear();

      // get all messages
      var eMails = GmailApp.getMessagesForThreads(
        GmailApp.search("label:" + labels[i].getName()))
          .reduce(function(a, b) {return a.concat(b);})
          .map(function(eMails) {
        return eMails.getFrom()
      });

      // sort and filter for unique entries
      var aEmails = eMails.sort().filter(function(el,j,a)
        {if(j==a.indexOf(el))return 1;return 0});

      // create 2D-array
      var aUnique = new Array();
      for(var k in aEmails) {
        aUnique.push([aEmails[k]]);
      }

      // add data to corresponding sheet
      sh.getRange(1, 1, aUnique.length, 1).setValues(aUnique);
    } catch (e) {
      emptyLabels.push(labels[i].getName());
    }
   }
   ss.toast("These sheets are empty: " + emptyLabels);
}

function getEmails() {
  // http://stackoverflow.com/a/12029701/1536038
  // get all messages
  var eMails = GmailApp.getMessagesForThreads(
    GmailApp.search('after:2012/1/14 before:2013/8/15'))
      .reduce(function(a, b) {return a.concat(b);})
      .map(function(eMails) {
    return eMails.getFrom()
  });

  // sort and filter for unique entries
  var aEmails = eMails.sort().filter(function(el,j,a)
    {if(j==a.indexOf(el))return 1;return 0});

  // create 2D-array
  var aUnique = new Array();
  for(var k in aEmails) {
    aUnique.push([aEmails[k]]);
  }

  // add data to sheet
  SpreadsheetApp.getActiveSheet().getRange(1, 1, aUnique.length, 1)
    .setValues(aUnique);
}

function getEmails() {
  // set spreadsheet and retrieve labels
  var query = 'YOUR GMAIL SEARCH QUERY GOES HERE',
    ss = SpreadsheetApp.getActiveSpreadsheet(),
    sh = ss.getSheetByName(query) || ss.insertSheet(query, ss.getSheets().length),
    uniqueEmails = {},
    errors = [],
    // max chunk size
    chunkSize = 500,
    currentChunk = 0,
    threads,
    messages,
    i,
    j,
    k,
    msg,
    tos;
  sh.clear();
  while (currentChunk === 0 || threads.length === chunkSize) {
    try {
      // grab threads that match the query one chunk at a time
      threads = GmailApp.search(query, chunkSize * currentChunk, chunkSize);
      // grab corresponding messages from the threads
      messages = GmailApp.getMessagesForThreads(threads);
      for (i = 0; i < messages.length; i++) {
        msg = messages[i];
        for (j = 0; j < msg.length; j++) {
          // get the from
          uniqueEmails[msg[j].getFrom()] = true;
          // get the reply to
          uniqueEmails[msg[j].getReplyTo()] = true;
          // grab from the to field as well
          // this has a bug for people with commas in their names
          // tos = msg[j].getTo().split(',');
          // for (k = 0; k < tos.length; k++) {
          //  uniqueEmails[tos[k]] = true;
          // }
        }
      }
      currentChunk += 1;
    } catch (e) {
      errors.push(e);
    }
  }
  // create 2D-array
  var aUnique = [];
  for (k in uniqueEmails) {
    aUnique.push([k]);
  }

  // add data to corresponding sheet
  sh.getRange(1, 1, aUnique.length, 1).setValues(aUnique);
}