Exchange Internet-facing Send connectors must specify a Smart Host.

From MS Exchange 2013 Edge Transport Server Security Technical Implementation Guide

Part of SRG-APP-000213

Associated with: CCI-001178

SV-84435r1_rule Exchange Internet-facing Send connectors must specify a Smart Host.

Vulnerability discussion

When identifying a "Smart Host" for the email environment, a logical Send connector is the preferred method.A Smart Host acts as an Internet-facing concentrator for other email servers. Appropriate hardening can be applied to the Smart Host, rather than at multiple locations throughout the enterprise.Failure to identify a Smart Host could default to each email server performing its own lookups (potentially through protective firewalls). Exchange servers should not be Internet facing and should therefore not perform any Smart Host functions. When the Exchange servers are Internet facing, they must be configured to identify the Internet-facing server that is performing the Smart Host function.

Check content

Review the Email Domain Security Plan (EDSP). Determine the Internet-facing connectors. Open the Exchange Management Shell and enter the following command: Get-SendConnector | Select Name, Identity, SmartHosts, DNSRoutingEnabled For each Send connector, if the value of SmartHosts does not return the Smart Host IP Address and the value for DNSRoutingEnabled is not set to False, this is a finding.

Fix text

Open the Exchange Management Shell and enter the following command: Set-SendConnector <'IdentityName'> -SmartHosts <'IP Address of Smart Host'> -DNSRoutingEnabled $false Note: The value must be in quotes. Repeat the procedures for each Send connector.

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