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The Exchange Simple Mail Transfer Protocol (SMTP) IP Allow List Connection filter must be enabled.


Finding ID Version Rule ID IA Controls Severity
V-259624 EX19-ED-000138 SV-259624r942186_rule Medium
Email system availability depends in part on best practice strategies for setting tuning configurations. Careful tuning reduces the risk that system or network congestion will contribute to availability impacts. Filters that govern inbound email evaluation can significantly reduce spam, phishing, and spoofed emails. Filters for messages from blank senders, known spammers, or zero-day attack modifications must be enabled to be effective. Having items identified in the Allow List causes other spam evaluation steps to be bypassed and therefore should be used only with an abundance of caution. If spammers were to learn of entries in the Allow List, it could enable them to plan a denial of service attack (or other attack) by spoofing that source.
Microsoft Exchange 2019 Edge Server Security Technical Implementation Guide 2024-01-10


Check Text ( C-63363r942184_chk )
Open the Exchange Management Shell and enter the following command:

Get-IPAllowListConfig | Select-Object -Property Name, Enabled

If the value for "Enabled" is not set to "True", this is a finding.

Note: "Enabled" set to "True" is the default value.
Fix Text (F-63271r942185_fix)
Open the Exchange Management Shell and enter the following command:

Set-IPAllowListConfig -Enabled $true