I FINALLY GOT THIS WORKING!
when sending an invoice to a customer, there is a centerfield where you can select into it as a sender or your company email as a sender. At some point we had added our company email as a sender. This causes some sort of a bug in the system and into its servers have issues with sending emails with other company domains in this Sender address. So I clicked the drop-down menu under sender and chose to delete email address, or better said the company’s email address, And only left the intuit email address as the sender. That is the default. Then I had to erase the last couple of characters on the customer’s email address so that it would think I was typing a new one. Then I retype the character characters I had deleted and immediately press send. The invoice sent without an issue anymore. New invoices sent without a problem. But invoices that you previously tried to send where you receive the message unable to reach, Will have to be sent in this way where you make sure that the sender is into it and that your company’s email is no longer an option as a sender, and you will have to delete the last few characters of your customer’s email address and retype them. Do not click anything else after you retype them other than send. If you click on anything else, you will have to erase the last few characters of the customer’s email address again before you click send. All new invoices are sending just fine without having to erase any characters in the customer’s email address. So again, this only applies to emails where you are sending a previously unsent invoice. I hope this helps someone else. And just FYI, the customer will receive the email and the from will indicate Your company‘s name at intuit.quickbooks.com, But if the customer clicks reply to the email, It will send it to whatever email you have selected as your company email in your company settings. So you will still receive emails from your customer. Into its email address it’s only used to send the invoice to them
