Go to Gmail and make sure 2-step verification is turned on.  Then select App Passwords, under select App, choose Other and type in Quickbooks.  Write down the generated password since Quickbooks won't allow it to be pasted.  Open Quickbooks and go to Send Forms, delete the original setup and create a new one.  When the first email is sent out, type in the new password that is for Quickbooks only and QB will save for subsequent uses.