Exchange messages with a blank sender field must be filtered.

Severity	Group ID	Group Title	Version	Rule ID	Date	STIG Version
medium	V-259610	SRG-APP-000261	EX19-ED-000124	SV-259610r961161_rule	2024-12-06	2

Description
By performing filtering at the perimeter, up to 90 percent of spam, malware, and other undesirable messages are eliminated from the message stream rather than admitting them into the mail server environment. Anonymous email (messages with blank sender fields) cannot be replied to. Messages formatted in this way may be attempting to hide their true origin to avoid responses or to spam any receiver with impunity while hiding their source of origination. Rather than spend resources and risk infection while evaluating them, it is recommended that these messages be filtered immediately upon receipt and not forwarded to end users.

Description

By performing filtering at the perimeter, up to 90 percent of spam, malware, and other undesirable messages are eliminated from the message stream rather than admitting them into the mail server environment. Anonymous email (messages with blank sender fields) cannot be replied to. Messages formatted in this way may be attempting to hide their true origin to avoid responses or to spam any receiver with impunity while hiding their source of origination. Rather than spend resources and risk infection while evaluating them, it is recommended that these messages be filtered immediately upon receipt and not forwarded to end users.

ℹ️ Check
This requirement is Not Applicable for SIPR enclaves. This requirement is Not Applicable if the organization subscribes to EEMSG or other similar DOD enterprise protections for email services. Open the Exchange Management Shell and enter the following command: Get-SenderFilterConfig \| Select-Object -Property Name, BlankSenderBlockingEnabled If the value of "BlankSenderBlockingEnabled" is not set to "True", this is a finding.

ℹ️ Check

This requirement is Not Applicable for SIPR enclaves. This requirement is Not Applicable if the organization subscribes to EEMSG or other similar DOD enterprise protections for email services. Open the Exchange Management Shell and enter the following command: Get-SenderFilterConfig | Select-Object -Property Name, BlankSenderBlockingEnabled If the value of "BlankSenderBlockingEnabled" is not set to "True", this is a finding.

✔️ Fix
Open the Exchange Management Shell and enter the following command: Set-SenderFilterConfig -BlankSenderBlockingEnabled $true