Rules/MAIL-003.dmarc-enforced.psd1
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@{ Id = 'MAIL-003' Title = 'DMARC is published and enforced for every custom mail domain' Area = 'EmailAuthDns' Severity = 'High' References = @( 'CIS Microsoft 365 Foundations Benchmark (DMARC records)' 'https://learn.microsoft.com/defender-office-365/email-authentication-dmarc-configure' ) Rationale = 'DMARC tells receiving servers what to do with mail that fails SPF/DKIM. A policy of none only monitors; quarantine or reject actually stops spoofing.' Remediation = 'Publish a _dmarc TXT record with at least p=quarantine (ideally p=reject) and rua reporting, after validating SPF and DKIM alignment.' Test = { param($Snapshot) $customDomains = @($Snapshot.EmailAuthDns | Where-Object { -not $_.isOnMicrosoft }) # Older snapshots have no isMailDomain field - treat those as mail domains. $mailDomains = @($customDomains | Where-Object { -not $_.PSObject.Properties['isMailDomain'] -or [bool]$_.isMailDomain }) $nonMailDomains = @($customDomains | Where-Object { $_.PSObject.Properties['isMailDomain'] -and -not [bool]$_.isMailDomain }) $notes = @() if ($nonMailDomains.Count -gt 0) { $notes = @('Not evaluated (no Email service): ' + (@($nonMailDomains | ForEach-Object { $_.domain }) -join ', ') + '. Consider publishing DMARC p=reject on non-mail domains as spoofing protection.') } if ($mailDomains.Count -eq 0) { return New-TLRuleResult -Status Pass -Evidence (@('No custom mail domains to check.') + $notes) } $bad = @($mailDomains | Where-Object { -not ($_.dmarc.present -and (@('quarantine', 'reject') -contains [string]$_.dmarc.policy)) }) if ($bad.Count -gt 0) { New-TLRuleResult -Status Fail -Evidence (@($bad | ForEach-Object { $detail = 'no DMARC record' if ($_.dmarc.present) { $detail = "policy 'p=$($_.dmarc.policy)'" } "$($_.domain): $detail" }) + $notes) } else { New-TLRuleResult -Status Pass -Evidence (@($mailDomains | ForEach-Object { "$($_.domain): p=$($_.dmarc.policy)" }) + $notes) } } } |