QuickBooks users had requested the feature of being able to set “To Be Emailed” or to email a invoice directly via QBI.
Intuit (makers of QuickBooks) was looking into being able to provide developers with this ability to implement via a third party program such as QBI.
Intuit hasnow stated that this will not be a provided feature due to the complexities involved, so unfortunately it is not a feature that can be provided with QBI due to QuickBooks restrictions.