Rules/MAIL-001.spf-configured.psd1
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@{ Id = 'MAIL-001' Title = 'Every custom mail domain publishes a strict SPF record' Area = 'EmailAuthDns' Severity = 'High' References = @( 'CIS Microsoft 365 Foundations Benchmark (SPF records for all domains)' 'https://learn.microsoft.com/defender-office-365/email-authentication-spf-configure' ) Rationale = 'Without SPF (or with +all), anyone can spoof mail from the domain. SPF must end in -all (hardfail) or at least ~all (softfail).' Remediation = 'Publish a TXT record "v=spf1 include:spf.protection.outlook.com -all" (plus any legitimate senders) on every custom mail domain.' 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 { $_.domain }) -join ', ') + '. Consider publishing "v=spf1 -all" and DMARC p=reject on non-mail domains as spoofing protection.') } if ($mailDomains.Count -eq 0) { return New-TLRuleResult -Status Pass -Evidence (@('No custom mail domains to check.') + $notes) } $bad = @($mailDomains | Where-Object { -not ($_.spf.present -and (@('hardfail', 'softfail') -contains [string]$_.spf.qualifier)) }) if ($bad.Count -gt 0) { New-TLRuleResult -Status Fail -Evidence (@($bad | ForEach-Object { $detail = 'no SPF record' if ($_.spf.present) { $detail = "qualifier '$($_.spf.qualifier)'" } "$($_.domain): $detail" }) + $notes) } else { New-TLRuleResult -Status Pass -Evidence (@($mailDomains | ForEach-Object { "$($_.domain): $($_.spf.qualifier)" }) + $notes) } } } |