Hi phil-carre, are you referring to sending invoices to customers from QuickBooks via your own email domain? Invoices sent from QuickBooks are sent from Intuits domain and cannot be personalised, unless using the send with Gmail feature.
I'm sending statements and they come from [email address removed]. In order for that to work without the emails being blocked or going to junk the SPF record (in the DNS) needs to say that intuit is allowed to send email on behalf of mydomain.com. I think the answer is that you add 'include:intuit.com' into the SPF record, but some people say that may not work due to the number of mail servers intuit is using exceeding what can be looked up, which causes an error.