So the underlying story of the Transition Team emails is they didn't read the TOS they agreed to when opening accounts on it. But the bigger story is Trump put in a Reagan Admin fixer/cleaner named Beckler, he was a lawyer before his appointment at the Guiliani Law Firm, and helped clean-up Ollie North Iran Contra mess back in the day for Reagan. Anyways this guy is put into the GSA and has an agreement with Trump Admin that should he get any requests from Mueller that he send all the emails to the Admin first so they can "clean them" of any Executive Privilege correspondences, then they'd send them back to the GSA and Beckler and that batch would be sent to Mueller. Problem being Beckler died. And Trump didn't replace him, so a 30 year career GSA employee has been acting director for 4-5 months now.
There was no legal basis for the agreement between Trump Admin and Beckler. Acting director didn't break any laws, in actuality he followed them. Trump team was acting on the belief that the emails from the Transition team period would have been "fixed" and thus very well could have been lying their asses off to Mueller all along - which is why there is the epic freak out right now.