ISM-1502 · September 2026
Blocking suspicious emails
Guidelines for email / Email gateways and servers / Blocking suspicious emails
Official control wording
Emails arriving via an external connection where the email source address uses an internal domain, or internal subdomain, are blocked at the email gateway.
Applicability
These are ASD’s applicability markings. Select and tailor controls for your system’s risk, classification and operating context with the system owner and authorising officer.
Implementation guidance
This control is included as official reference material. We have not published a reviewed Kubernetes implementation mapping for it. Browse the 23 guides with bounded public mappings.
Official source
ASD’s ISM OSCAL v2026.09.4 · Original catalogue JSON · Pinned checksums and edition details
Control source identifier: ism-1502. Check the official release before relying on this snapshot for an assessment.
Official control wording and applicability: Australian Signals Directorate, © Commonwealth of Australia 2026. September 2026 ISM, OSCAL v2026.09.4, reproduced under CC BY 4.0. Formatting is adapted for this website.
Latticework Systems’ implementation guidance is our interpretation. Provenance and scope.