SharePoint alerts are important part of end user functions for SharePoint sites. Alerts can be created for Lists, Libraries, folders and individual items. You can create alerts for yourself and others. In SharePoint Online you can not send alerts to mail-enabled Security Groups by default. You must add the Mail-Enabled security Group one SharePoint group with view permissions. SharePoint Alerts will work. If you do not want to add the group to SharePoint then you can use the Outlook Rules to forward email to the group. SharePoint workflow can also be used to send email as well.