Section 8A. A distributor duly licensed in this commonwealth may sell fuel tax-free to another person who is licensed as a distributor in this commonwealth. He may sell fuel tax-free to any person who is a licensed distributor in another state, provided, that the entire quantity purchased is to be exported forthwith from this commonwealth prior to use or resale, and provided, further, that such person is licensed by the commissioner as an unclassified exporter.