This Google Script, originally published by @rboyd, scans for lengthy emails in your Gmail mailbox (messages that have more than 100 words) and sends an auto-reply requesting the sender to resend the email after editing to less than 100 words. The long email is archived (moved away from the Inbox) after the auto-reply has been sent. You can set it up as a trigger to auto-run every 15 minutes.
Also see: Email Auto-responder for Gmail
// Credit: https://gist.github.com/rboyd/5027691
function deleteLongEmails() {
var WORDLIMIT = 100;
// Process only new emails in inbox that have not been read and receive in the last day
var threads = GmailApp.search('to:me is:unread in:inbox newer_than:1d');
for (var i = 0; i < threads.length; i++) {
// Ignore email conversations
if (threads[i].getMessageCount() == 1) {
var msg = threads[i].getMessages()[0];
var word_count = msg.getPlainBody().split(' ').length;
if (word_count > WORDLIMIT) {
msg.reply('Your email is too long. Please resend after editing it to less than 100 words.');
GmailApp.moveThreadToArchive(threads[i]);
}
}
}
}