Hi @Dee Noyes
The fact that the cc'd emails have reached your inbox shows that the QB/Intuit servers have done their bit - the emails have been sent out. The problem lies in the workings (or not) of email.
QB/Intuit's servers probably send out millions of emails a day. Every now & again, some of their addresses get blacklisted by other email servers (either intermediate or end user) - essentially marked as senders of spam. When that happens, most end-users will find the QBO emails in their spam/junk folders. However, many corporate systems will either quarantine the emails or delete them without further checks.
QB/Intuit can/should be constantly monitoring the published blacklists & getting their servers removed. How efficient they are at doing that is a question you can probably answer yourself.
If customers cannot check their spam/junk folders your only viable workaround is download & send the invoices from your own email account (or cc/fwd as you have done). That will be much more reliable as your customer's email system will probably recognise your address as a contact & be more likely to allow emails through.
Hope this helps (or at least, explains).
