The default message format must be set to use Plain Text.

Severity	Group ID	Group Title	Version	Rule ID	Date	STIG Version
medium	V-251866	SRG-APP-000516	DTOO314	SV-251866r811197_rule	2022-03-11	2

Description
Outlook uses HTML as the default email format. HTML format poses a security risk by embedding information into the email itself, which could allow for release of sensitive information. If a user attempted to insert an HTML link into an email message, the link itself may direct to a malicious website. By sending emails in HTML format, the recipient could be subject to becoming infected by the malicious website.

Description

Outlook uses HTML as the default email format. HTML format poses a security risk by embedding information into the email itself, which could allow for release of sensitive information. If a user attempted to insert an HTML link into an email message, the link itself may direct to a malicious website. By sending emails in HTML format, the recipient could be subject to becoming infected by the malicious website.

ℹ️ Check
Verify the policy value for User Configuration >> Administrative Templates >> Microsoft Outlook 2016 >> Outlook Options >> Mail Format >> Internet Formatting >> Message Format "Set message format" is "Enabled: Plain Text". Procedure: Use the Windows Registry Editor to navigate to the following key: HKCU\Software\Policies\Microsoft\Office\16.0\outlook\options\mail Criteria: If the value EditorPreference is REG_DWORD = 65536 (dec), this is not a finding.

ℹ️ Check

Verify the policy value for User Configuration >> Administrative Templates >> Microsoft Outlook 2016 >> Outlook Options >> Mail Format >> Internet Formatting >> Message Format "Set message format" is "Enabled: Plain Text". Procedure: Use the Windows Registry Editor to navigate to the following key: HKCU\Software\Policies\Microsoft\Office\16.0\outlook\options\mail Criteria: If the value EditorPreference is REG_DWORD = 65536 (dec), this is not a finding.

✔️ Fix
Set the policy value for User Configuration >> Administrative Templates >> Microsoft Outlook 2016 >> Outlook Options >> Mail Format >> Internet Formatting >> Message Format "Set message format" to "Enabled: Plain Text".