Within Gmail, is there any way to automatically forward an email when I apply a label?Gmail filters appear to only work with new emails. For my needs, applying the label is a manual process after the email was received.
How can I automatically forward Gmail emails when a label is applied?
gmail;gmail filters
Here is an Apps Script solution. Save it, changing the label and  recipient, and set a trigger to run this function every 5 minutes. It searches for threads with the given label that were created after the last time the script ran. In each, it forwards the first message to the given address. function autoForward() {  var label = 'forwardthis';  var recipient = 'forward@gmail.com';  var interval = 5;          //  if the script runs every 5 minutes; change otherwise  var date = new Date();  var timeFrom = Math.floor(date.valueOf()/1000) - 60 * interval;  var threads = GmailApp.search('label:' + label + ' after:' + timeFrom);  for (var i = 0; i < threads.length; i++) {    threads[i].getMessages()[0].forward(recipient);  // only the 1st message  }}I add some variations, replacing the line with only the 1st message:Forward every message in the threadvar messages = threads[i].getMessages();for (var j = 0; j < messages.length; j++) {  messages[j].forward(recipient);}Forward the last message in the threadvar messages = threads[i].getMessages();messages[messages.length - 1].forward(recipient);