回帖：根据SCL分级，只有打分为6的会进隔离邮箱，太高会被直接删除，太低会被放行到用户的垃圾邮箱或收件箱。
SCL is 8 or higher Silently delete the message.
SCL is 7 Reject the message with an NDR.
SCL is 6 Quarantine the message.
SCL is 5 Deliver the message to the user's Junk Email folder.
SCL is 4 or lower Deliver the message to the user's Inbox.
你需要自己设置这个隔离邮箱。
https://technet.microsoft.com/zh-cn/library/bb123746%28v=exchg.160%29.aspx