That's guano.
Once the FBI knows about the account, the fact the communicants were viewing each others drafts instead of exchanging messages between separate accounts is irrelevant. They'll go to the access logs and trace the IP addresses and lay out the exchanges on a neat geographic timeline.
The critical error occurred when Broadwell sent the intimidating emails to Jill Kelley. That sort of amusement called for much higher levels of security than simply exchanging love notes on Gmail high enough that you must assume the FBI will get the IP from which each message was sent, yet will not get you. Possible, but very inconvenient. Broadwell f'up up, pure and simple. If she wanted to intimidate Kelley, it needed to be from a totally isolated (geographically and temporally) account.
I am almost NOT BUYING the story of the “threatening” e-mails sent between the tramps........something’s not right.