let To_Email = "PUTYOUREMAILHERE@yahoo.com"; // email to send the form data to

/**
 * This fn is the entry point.
 */
function postData(e) {

  try {
    Logger.log(e); // the Google Script version of console.log see: Class Logger

    let emailData = e.parameters; // just create a slightly nicer variable name for the data

    if (emailData.invite_code != "123456") { // validate invite code before saving data
      Logger.log("Incorrect Invite Code");
      return ContentService
          .createTextOutput(JSON.stringify({"result":"error", "message": "Sorry, your invite code (" + emailData.invite_code + ") is incorrect."}))
          .setMimeType(ContentService.MimeType.JSON);
    }

    record_data(e);

    MailApp.sendEmail({
      to: To_Email,
      subject: "A new guest RSVP'd for your wedding",
      replyTo: String(emailData.email), // This is optional and reliant on your form actually collecting a field named `email`
      htmlBody: formatMailBody(emailData)
    });

    return ContentService    // return json success results
          .createTextOutput(JSON.stringify({"result":"success","data": JSON.stringify(e.parameters) }))
          .setMimeType(ContentService.MimeType.JSON);
  } catch(error) { // if error return this
    Logger.log(error);
    return ContentService
          .createTextOutput(JSON.stringify({"result":"error", "message": "Sorry, there is an issue with the server."}))
          .setMimeType(ContentService.MimeType.JSON);
  }
}


/**
 * This fn inserts the data received from the html form submission
 * into the sheet. e is the data received from the POST
 */
function recordData(e) {
  Logger.log(JSON.stringify(e)); // log the POST data in case we need to debug it
  try {
    let doc     = SpreadsheetApp.getActiveSpreadsheet();
    let sheet   = doc.getSheetByName('responses'); // select the responses sheet
    let headers = sheet.getRange(1, 1, 1, sheet.getLastColumn()).getValues()[0];
    let nextRow = sheet.getLastRow()+1; // get next row
    let row     = [ new Date().toUTCString() ]; // first element in the row should always be a timestamp
    // loop through the header columns
    for (let i = 1; i < headers.length; i++) { // start at 1 to avoid Timestamp column
      if(headers[i].length > 0) {
        row.push(e.parameter[headers[i]]); // add data to row
      }
    }
    // more efficient to set values as [][] array than individually
    sheet.getRange(nextRow, 1, 1, row.length).setValues([row]);
  }
  catch(error) {
    Logger.log(error);
    Logger.log(e);
    throw error;
  }
  finally {
    return;
  }
}


/**
 * This method is just to prettify the email.
 */
function formatEmailBody(obj) { // function to spit out all the keys/values from the form in HTML
  let result = "";
  for (let key in obj) { // loop over the object passed to the function
    result += "<h4 style='text-transform: capitalize; margin-bottom: 0'>" + key + "</h4><div>" + obj[key] + "</div>";
    // for every key, concatenate an `<h4 />`/`<div />` pairing of the key name and its value, 
    // and append it to the `result` string created at the start.
  }
  return result; // once the looping is done, `result` will be one long string to put in the email body
}

<form class="gform pure-form pure-form-stacked"
method="POST" 
data-email="example@email.net"
action="https://script.google.com/macros/s/AKfycbx1AQpIsZzuNX3VWwLCucruNuLytoTbFpWMZ4ndpfxfRztHMn8/exec"> 
<!-- change the form action to your script editor published url -->
<h2 class="content-head is-center">The Kirk Wedding</h2>
<aside>
<p>
We would <em>love</em> to have you at our wedding! </p>
<p>Please use the <b><em>RSVP form</em></b>
to let us know you'll be there.
</p>
</aside>
<div class="input-container">
<div class="col-md-6 col-sm-6">
<div class="form-input-group">
<i class="fa fa-envelope"></i>
<label>Email: </label>
<input type="email" name="email" class="" placeholder="Your email" required>
</div>
<div class="col-md-6 col-sm-6">
<div class="form-input-group">
<i class="fa fa-user"></i>
<label>Full Name: </label>
<input name="name" class="" placeholder="Your name" required>
</div>
</div>
</div>
<div class="row">
<div class="col-md-6 col-sm-6">
<div class="form-input-group">
<i class="fa fa-users"></i>
<label>Husband/Wife or kids: </label>
<input type="number" name="extras" class="" min="0" max="4" placeholder="" required>
</div>
</div>
<div class="col-md-6 col-sm-6">
<div class="form-input-group">
<i class="fa fa-key"></i>
<label>Invite Code: </label>
<input type="number" name="invite_code" id="invite_code" class="" min="0" placeholder="Invite code" required>
</div>
</div>
<div class="form-input-group">
<button class="button-success pure-button button-xlarge">
<i class="fa fa-paper-plane"></i>&nbsp;Send</button>
</div>
</div>
</div>
</form>