Thanks for joining in this thread @MikeS2017,

I'd like to share some information about changing the outgoing email address for invoices.

Changing the email address when sending sales forms in QuickBooks Online is currently unavailable. 

Your thoughts are important to us. We'll make sure to take note of your suggestion and use it to improve the flow when sending invoices to your customers in QuickBooks Online. 

In the meantime, I suggest visiting our Blog site to know the latest updates as well other references while working in QuickBooks.

Your suggestion would be a big help! Fill me in if you have any questions or concerns about QuickBooks Online. I'm always here to help. Have a good one.