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

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-221217	EX16-ED-000160	SV-221217r612603_rule		Medium

Description
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.

Description

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.

STIG	Date
Microsoft Exchange 2016 Edge Transport Server Security Technical Implementation Guide	2020-12-10

Details

Check Text ( C-22932r411777_chk )
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.

Check Text ( C-22932r411777_chk )

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 (F-22921r411778_fix)
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 single quotes. Repeat the procedures for each send connector.