This may be a dumb question, but emailing my invoices have been working terrific and have not had a problem with it at all and was just stuck on one thing. I am having trouble with one email address that keeps getting sent back to me as Undelivered Mail Returned to Sender which does happen when there isn't a valid email or their firewall restrictions are not allowing them to be sent to them so then I either contact their administrator or I use the email that was sent back to me and go in just print off their invoice and mail it to them. I have one email that keeps getting sent back to me and I can't for the life of me find the email and the corresponding customer account so I am wondering if there is anyway I can tell which invoices got emailed and which ones didn't or there was another way of finding my customer in the system so I can get them their invoices? I have it narrowed down to a list of about 25 possible ones but am having trouble so any feedback would be much appreciated. Thanks!