Microsoft BCL or Bulk Complaint Level Values for Email



  • Microsoft maintains an internal SPAM detection and ranking system that uses an internal ranking called a BCL value. This rating is exposed in the X-Microsoft-Antispam header of every message. This score comes from both an internal mechanism and Microsoft pulling third party (external) ranking information.

    BCL Value Description
    0 The message isn't from a bulk sender.
    1, 2, 3 The message is from a bulk sender that generates few complaints.
    4, 5, 6, 7 The message is from a bulk sender that generates a mixed number of complaints.
    8, 9 The message is from a bulk sender that generates a high number of complaints

    https://docs.microsoft.com/en-us/office365/SecurityCompliance/bulk-complaint-level-values