CISA.MS.EXO.1.1: Automatic forwarding to external domains SHALL be disabled.
| ID | CISA.MS.EXO.1.1 |
| Severity | High |
| Suite | CISA SCuBA baselines |
| Product | Exchange Online |
| Feature | Mail flow |
| Security area | Email and collaboration protection |
| Resource type | Domain |
| User impact of fixing | Medium |
| Effort to fix | Low |
| Benchmark | CISA SCuBA Secure Configuration Baselines for Microsoft 365 ScubaGear main, 2026-10-11, MS.EXO.1.1 (SHALL) |
| Framework controls | cisa-scuba:MS.EXO.1.1nist-800-53-r5:AC-4 Information Flow Enforcement |
| MITRE ATT&CK | T1114.003, T1048, T1567 |
| Reads from | Exchange Online |
What this checks and how to fix it
Section titled “What this checks and how to fix it”Automatic forwarding to external domains SHALL be disabled.
Rationale: Adversaries can use automatic forwarding to gain persistent access to a victim’s email. Disabling forwarding to external domains prevents this technique when the adversary is external to the organization but does not impede legitimate internal forwarding.
Remediation action:
Section titled “Remediation action:”To disable automatic forwarding to external domains:
- Sign in to the Exchange admin center.
- Select Mail flow, then Remote domains.
- Select Default.
- Under Email reply types, select Edit reply types.
- Clear the checkbox next to Allow automatic forwarding, then click Save.
- Return to Remote domains and repeat steps 4 and 5 for each additional remote domain in the list.
Related links
Section titled “Related links”- Exchange admin center - Remote domains
- CISA 1 Automatic Forwarding to External Domains - MS.EXO.1.1v1
- CISA ScubaGear Rego Reference
Mito check, based on CISA ScubaGear. Author: soulemike; contributors: merill. Open-source licences.
Open-source licences. CIS Benchmark material © Center for Internet Security, Inc.; CISA SCuBA baselines are public domain (CC0).
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