Spam confidence level

What it means

Microsoft's spam filtering stamps an SCL value of -1, or 0 to 9, in the X-Forefront-Antispam-Report header, and a value of 5 or higher generally indicates the message was considered bad. Microsoft now documents that in cloud organisations the value no longer determines whether a message is spam or high confidence spam, nor the action taken: those come from categorisation and other signals, shown in the same header as CAT (category) and DIR (direction).

In the cloud, SCL is used mainly in mail flow rules, to request a filtering bypass (-1), treat mail as spam (5 or 6) or as high confidence spam (9). Its main purpose is on-premises Exchange, where thresholds in the Content Filter agent and the Junk Email threshold still read it.

Read SCL with CAT and the bulk complaint level when diagnosing Microsoft placement.