Let's fix this error so your customers can receive your emails from QuickBooks, @trconstructionma.
Here are the possible reasons why your customers aren't receiving your emails and on how to resolve them:
You've imported QuickBooks Desktop data into a QuickBooks Online company.If this is the case, you'll need to reset your email address from the Account and Settings. If it's not, proceed to the next solution.
Let your customers check their junk mail and spam folders. If the email is still not found, clear and then re-enter your email address from the Account and Settings by clearing the Company email field and enter the desired address.
If none of those solutions works, you'll need to have the QuickBooks Online mail server hostnames and IP addresses be added to your outgoing mail servers.