Google Apps Script for Gmail, creates a label that matches all threads where you are the last sender. Useful for finding email messages in your mailbox that are still awaiting a response from the customer. Credit @GSAPU.
function label_last_sent_message() {
var emailAddress = Session.getEffectiveUser().getEmail();
Logger.log(emailAddress);
var EMAIL_REGEX = /[a-zA-Z0-9\._\-]+@[a-zA-Z0-9\.\-]+\.[a-z\.A-Z]+/g;
var label = GmailApp.createLabel("LastSentMessage");
var d = new Date();
d.setDate(d.getDate() - 7);
var dateString = d.getFullYear() + "/" + (d.getMonth() + 1) + "/" + d.getDate();
threads = GmailApp.search("in:Sent after:" + dateString);
for (var i = 0; i < threads.length; i++)
{
var thread = threads[i];
var lastMessage = thread.getMessages()[thread.getMessageCount()-1];
var lastMessageSender = lastMessage.getFrom().match(EMAIL_REGEX)[0];
if ((thread.getMessageCount() > 1) && (lastMessageSender == emailAddress))
{
thread.addLabel(label);
}
}
}