If you have looked at Exchange Server’s anti-spam features or taken a peek at the headers of an email sent through an Exchange server you have probably encountered the term SCL before.
SCL stands for Spam Confidence Level. It is the “score” that Exchange Server anti-spam assigns to an email based on the email’s contents. This score is then used to make decisions as to how to handle suspected spam based on the thresholds that the Exchange administrator configures.
Having a detailed understanding of the SCL and how it is used in Exchange Server anti-spam will allow an email administrator to get good performance from their anti-spam deployment.