This is happening to me too. EVERY invoice sent from12/13 is UNDELIVERABLE. It is NOT an error in the customers' email addresses.  WHEN IS THIS GOING TO BE FIXED? THIS IS A KNOW ISSUE.

Saving every invoice as a PDF and then sending them from another email account is time-consuming and a TEMPORARY FIX. You're telling me that in 5 days your engineers can't fix the problem?

FROM QB Support on 12/15:

Good day!
Thank you for contacting us. Your account has been affected by the ongoing investigation. The issue has been reported already to the engineering department, the highest department we have, our back-end team.

Now, they are expediting the process, thus, they are kind of prioritizing the permanent fix of your issue. One of them is already been assigned to work on it.

However, I was advised to close the case I have created based on my level, a tier 1 technical support, since this will create a duplicate entry on their bucket which might lead to the delayed fix due to confusion for, they create their own ticketing too.

Now, with all your permission, I'll be now tagging our case as closed not to cause any delays processing the escalated case. Just want to make sure that everything will be processed as soon as possible.

Also, closing the case will not mean that you won't receive any updates regarding on the investigation. The engineering department will still send an email for any update of the status of the investigation.

We thank you for your patience and understanding. This is in reference to the case with ticket number: 1591876356
Investigation number: INV-71760