Creates a defined label from contacts in a defined email which then can use said label to message that group of contacts.

gmail_create_label_from_message_contacts.js

/*
Copyright © 2019 Cody Antonio Gagnon
Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the “Software”), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
*/

// enter your GMAIL_LABEL and CONTACTS_LABEL here:
var GMAIL_LABEL = "group contacts";
var CONTACTS_LABEL = "";
// if your contacts are in the TO: field (not the FROM: field) set this variable to true
var TO = true;

//TODO: Get email via searchterm

// Log all the subject lines in the first thread of your inbox
function myFunction() {
  var thread = GmailApp.search("in:" + GMAIL_LABEL, 0, 1)[0];
  var message = thread.getMessages()[0]; // get first message from search
  if(TO){
    return message.getTo();
  } else {
    return message.getFrom();
  }
  // for (var i = 0 ; i < messages.length; i++) {
  //   Logger.log("subject: " + messages[i].getSubject());
  //   return "subject: " + messages[i].getSubject()
  // }
}

function newFunction(){
  Logger.log("hello, world"); 
}

//TODO: check if a label exists -> if it doesn't then create a new one; otherwise use existing