That's pretty explicit.
The word “forbidding” can be attributed to Patrick Howley, the writer. Valerie Jarrett goes on to say that “if you do use private email, you have to turn it over”.
Evidently, it was “allowed”, but discussion of the private server is more to the point of the problem.
I didn’t read the whole thing. So far, they have come up with mostly uninteresting text and a little comedy in these emails. There is the illegal point to be made that all communication by an SoS is classified, by virtue of the office.
Hillary is an idiot. She took the people’s information, illegally removed the information from government property, and illegally stored it on an illegal personal server that was improperly secured, and then passed the server around to a couple of rag tag IT locations in Colorado and New Jersey, who had no security clearance, and she passed along the thumb drives of the contents to her personal lawyer who had no security clearance, and who himself improperly stored the contents in an improperly secured location— his own damn safe at the office.
This is RICH, really rich.
And yet at least once a week Valerie Jarrett emailed Hillary Clinton using the private email address and took no managerial action to enforce the guidance of no private email addresses for Cabinet secretaries.
If that is not in writing it's simply Jarrett poking Hillary with a sharp stick.