Uncheck the "Send mail for this update" on the Jira Bulk Edit screen.
// ==UserScript==
// @name Jira Uncheck bulk edit emailer
// @namespace randomecho.com
// @description Uncheck the "Send mail for this update" on the Jira Bulk Edit screen.
// @include https://*.atlassian.net/secure/views/bulkedit/BulkEditDetails.jspa
// @include */secure/views/bulkedit/BulkEditDetails.jspa
// @grant none
// @copyright 2017 Soon Van
// @author Soon Van - randomecho.com
// @license http://opensource.org/licenses/BSD-3-Clause
// @version 1.0
// ==/UserScript==
var sendBulkEmail = document.getElementById('sendBulkNotificationCB');
sendBulkEmail.checked = false;