What should I do? Suddenly all of my emailed invoices have a red warning notice "Delivery Issue" when I try to send. I've had one finally send after about 3 days.

I am having the same issue. I dont get the undelivered notification though… mine are sending and then 3 seconds later say they weren’t sent. It’s really annoying and needs to be fixed. 

Thank you for reaching us, blueknightroof.

I know how important it is to send your invoices to your customers on time. I checked our system and found that there is an ongoing investigation with undelivered invoices.

Our engineers are looking into the problem in order to find a long-term solution so you can resume sending invoices. In the meantime, I recommend reaching our Support Team so that you can be included to the list of users who are impacted by this problem and receive important updates.

Thank you for your patience. Just leave us a comment if you have other concerns about invoices. We'll be here to help. Have a great day!