Who knows? They probably dumped it off on them as if that name means anything any more.
The crux of it is the concept of an open internet email system being any level of secure from a standpoint of being legitimate for transmittal of classified information is not something that should be entertained on its face at all.
IF then the FBI is involved, it should be under the assumption a criminal act(s) has/have occurred in ALLOWING porting of classified information to an open internet system. It has no bearing otherwise except to survey the damage done. The STANDARD assumption would be NOT IF a hack occurred, but when and by whom and how many organizations.
If it were you or I that had allowed classified (de-marked, BTW) information to flow through our email accounts, the FBI wouldn’t be “investigating the e-mail system’s security”. They would be “investigating” how many crimes you and me would be charged with.