So today is the first day I have received some sort of notification regarding this issue, not from QB but from a Local company here that provides accounting packages to companies. This is what they sent. So I'm wondering how they were notified but QBO is not letting users know unless you on this thread?

We are emailing you today because we noticed invoices you recently sent didn’t go through and we have found out that QuickBooks IP Addresses are being blocked by the public spam blocklist called Spamcop. The result is some QuickBooks invoices are not being received by the customers because of the spam block technology that has identified QuickBooks IP addresses as spam. Here’s how you can check the delivery status of your recent invoices :

1. Go To your Dashboard >> Getting things Done >> Tasks
2. Sales >> Invoices Tab >> Status will say Undelivered

Intuit are dealing with this issue with High Priority. Until The Engineers have sorted out this issue, there are a few ways that you can solve this problem:

1. You can save your invoice as a PDF and send it via email through your business or other email address.
2. You can send your customer a link to their invoice through SMS or a messenger service. Simply click on “save and share link” then select “copy link” and paste it in your SMS, messenger service or Email.
3. If you have a gmail or G-suite email account, you can use the Send with Gmail feature to send invoices from your own address
4. If you don't have a gmail address  You can set up a free account and use that account to send with Gmail feature to send invoices from your own address

As soon as Intuit have a fix for this issue, we will send you an update.