Exchange auto-forwarding email to remote domains must be disabled or restricted.

Severity	Group ID	Group Title	Version	Rule ID	Date	STIG Version
medium	V-259651	SRG-APP-000038	EX19-MB-000021	SV-259651r960801_rule	2024-08-22	2

Description
Attackers can use automated messages to determine whether a user account is active, in the office, traveling, and so on. An attacker might use this information to conduct future attacks. Verify Automatic Forwards to remote domains are disabled, except for enterprise mail that must be restricted to forward only to .mil and .gov. domains. Before enabling this setting, configure a remote domain.

ℹ️ Check
Note: This requirement is not applicable on classified or completely closed networks. For Non-Enterprise Mail: Open the Exchange Management Shell and enter the following command: Get-RemoteDomain \| Select-Object -Property Identity, AutoForwardEnabled If the value of AutoForwardEnabled is not set to "False", this is a finding. For Enterprise Mail: If the value of "AutoForwardEnabled" is set to "True", this is not a finding. and In the Exchange Management Shell, enter the following command: Get-RemoteDomain If the value of "RemoteDomain" is not set to ".mil" and/or ".gov" domain(s), this is a finding.

ℹ️ Check

Note: This requirement is not applicable on classified or completely closed networks. For Non-Enterprise Mail: Open the Exchange Management Shell and enter the following command: Get-RemoteDomain | Select-Object -Property Identity, AutoForwardEnabled If the value of AutoForwardEnabled is not set to "False", this is a finding. For Enterprise Mail: If the value of "AutoForwardEnabled" is set to "True", this is not a finding. and In the Exchange Management Shell, enter the following command: Get-RemoteDomain If the value of "RemoteDomain" is not set to ".mil" and/or ".gov" domain(s), this is a finding.

✔️ Fix
For Non-Enterprise Mail: Open the Exchange Management Shell and enter the following command: Set-RemoteDomain -Identity <'IdentityName'> -AutoForwardEnabled $false Note: The <IdentityName> value must be in quotes. For Enterprise Mail: New-RemoteDomain -Name <NewRemoteDomainName> -DomainName <SMTP Address> Note: <NewRemoteDomainName> must either be a .mil or .gov domain. Set-RemoteDomain -Identity <'RemoteDomainIdentity'> -AutoForwardEnabled $true Note: The <RemoteDomainIdentity> value must be in quotes.

✔️ Fix

For Non-Enterprise Mail: Open the Exchange Management Shell and enter the following command: Set-RemoteDomain -Identity <'IdentityName'> -AutoForwardEnabled $false Note: The <IdentityName> value must be in quotes. For Enterprise Mail: New-RemoteDomain -Name <NewRemoteDomainName> -DomainName <SMTP Address> Note: <NewRemoteDomainName> must either be a .mil or .gov domain. Set-RemoteDomain -Identity <'RemoteDomainIdentity'> -AutoForwardEnabled $true Note: The <RemoteDomainIdentity> value must be in quotes.