Rocket.Chat/app/lib/server/functions/checkEmailAvailability.js

import { Meteor } from 'meteor/meteor';
import s from 'underscore.string';
import { escapeRegExp } from '@rocket.chat/string-helpers';

export const checkEmailAvailability = function(email) {
	return !Meteor.users.findOne({ 'emails.address': { $regex: new RegExp(`^${ s.trim(escapeRegExp(email)) }$`, 'i') } });
};