Delivery Monitor has been a great tool. It shows how much email is delivered by a bunch of ISPs - probably more than even needed. Unfortunately it looks like it is closing it's service so I'm searching for a replacement. Return Path looks good too but looks like it is aimed for bigger businesses and is really really expensive. MailMonitorApp.com looks pretty basic but is very reasonable and has a free trial so I think I'll give that a shot. Sorry to see Delivery Monitor close its doors.