NIST 800-53 REV 5 • SYSTEM AND INFORMATION INTEGRITY
SI-8 — Spam Protection
Employ spam protection mechanisms at system entry and exit points to detect and act on unsolicited messages; and Update spam protection mechanisms when new releases are available in accordance with organizational configuration management policy and procedures.
Supplemental Guidance
System entry and exit points include firewalls, remote-access servers, electronic mail servers, web servers, proxy servers, workstations, notebook computers, and mobile devices. Spam can be transported by different means, including email, email attachments, and web accesses. Spam protection mechanisms include signature definitions.
Practitioner Notes
Protect your email system from spam, which is not just an annoyance but a primary delivery mechanism for phishing and malware.
Example 1: Configure Exchange Online Protection (EOP) in M365 with anti-spam policies. Set the spam confidence level (SCL) thresholds, enable bulk email filtering, and configure quarantine policies. Review quarantined messages regularly for false positives.
Example 2: Deploy a third-party email security gateway (Proofpoint, Mimecast, Barracuda) in front of your email system. Configure it to check sender reputation, validate SPF/DKIM/DMARC records, and scan attachments before delivery. Block emails from known spam sources.