This email is from Stan Greenberg who was a major political strategist to Bill Clinton and seems to still be giving a lot of advice to HRC and her team.
He's not really talking about Hillary's "systemic corruption," but rather is trying to open a conversation where Hillary can set herself apart from the "systemically corrupt" system.
She can't of course, because she's corrupt -- but I don't read this email as Greenberg calling her corrupt.