People are responding to quotes but the email comes back unable to deliver Error, unable to deliver, address not found

Hello rockinghamtreese,

Welcome to Community!  Getting a message that QuickBooks Online is unable to send estimates due to a delivery error, can cause some concern.   I would be happy to provide some insight here!

It's essential to ensure the email address is accurate on your customer profile.  If you create a transaction with a typo in the customer email and try to send, the email will fail due to the error, and an undelivered message will appear.  In addition, if you open an invoice and edit the email without resending the invoice, the banner will remain as undelivered and sent.  The best course of action is to proceed to the customer profile and make any necessary changes to their email address, and all additional emails that may be used as Cc/Bcc.  Otherwise, the error will reappear with each new transaction.  Please make sure the email is valid in both the customer profile and on the invoice. 

Our Engineers will work on a fix to remove the error from this scenario in the future.

Feel free to reach out again, if you have other questions.  We would be glad to help!