The Original SCL rating is 5 and that's the reason that it is quarantained. Maybe it can configured better or different, but this is what it is now.

X-MS-Exchange-Organization-SCL: -1
X-MS-Exchange-Organization-Original-SCL: 5

Identifies the original SCL of a quarantined message when it first entered the Exchange organization.
Identifies the SCL of the message. The possible SCL values are from 0 through 9. A larger value indicates a suspicious message. The special value -1 exempts the message from processing by the Content Filter agent. For more information, see Content Filtering.