M365EXO-014: Approved sending IP list maintained (MS.EXO.2.1)
- Platform
- Entra ID / M365
- Category
- Advanced Threat Protection
- Severity
- Medium
- Zero Trust pillar
- Applications & Workloads (weight 1)
- Golden fixtures
- 2
- Branch coverage
- Observed: fixtures prove the verdicts they exercise
- Provenance
- baseline
What it checks
SCuBA MS.EXO.2.1 requires that a list of approved IP addresses for sending mail be maintained, which forms the basis of an accurate SPF record. The approved sender list is the authoritative input that determines which hosts may legitimately send mail for each domain. Without a maintained list, an SPF policy cannot be scoped correctly and either fails to block spoofers or blocks legitimate senders.
Recommended value
A documented, current list of all approved sending sources per domain (Exchange Online include plus any third-party senders), reflected in the published SPF record
Remediation
Inventory every system that legitimately sends email on behalf of each accepted domain, including Exchange Online (spf.protection.outlook.com), marketing platforms, ticketing systems, and on-premises relays. Record this approved sender list as the source of truth and ensure the published SPF record references exactly those sources. Review the list whenever a new sending service is onboarded or retired so the SPF record stays accurate.
Fixture-proven verdicts
Every verdict below is proven by a golden fixture in the module's gating test suite. This table derives from the last green run; it cannot be edited by hand.
| Scenario | Expected verdict |
|---|---|
| always-warn | WARN |
| throttled | Not Assessed |
Framework mappings
- NIST SP 800-53
- SI-8
- MITRE ATT&CK
- T1566.001