EMAIL-004: MTA-STS Policy
- Platform
- Google Workspace
- Category
- Advanced Threat Protection
- Severity
- Medium
- Zero Trust pillar
- Applications & Workloads (weight 1)
- Golden fixtures
- 3
- Branch coverage
- Observed: fixtures prove the verdicts they exercise
- Provenance
- baseline
What it checks
Mail Transfer Agent Strict Transport Security (MTA-STS) prevents TLS downgrade attacks and man-in-the-middle interception of email in transit by requiring authenticated TLS connections
Recommended value
MTA-STS TXT record published and policy hosted at https://mta-sts.<domain>/.well-known/mta-sts.txt
Remediation
Publish _mta-sts.<domain> TXT record with v=STSv1; id=<unique_id> and host MTA-STS policy file at https://mta-sts.<domain>/.well-known/mta-sts.txt
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 |
|---|---|
| clean | PASS |
| known-bad | WARN |
| throttled | Not Assessed |
Framework mappings
- NIST SP 800-53
- SC-8, SC-8(1)
- CIS Benchmark
- 2.4
- MITRE ATT&CK
- T1557, T1040