Read EMail as plain text must be enforced.

Severity	Group ID	Group Title	Version	Rule ID	Date	STIG Version
medium	V-251863	SRG-APP-000516	DTOO214	SV-251863r811196_rule	2022-03-11	2

Description
Outlook can display email messages and other items in three formats: plain text, Rich Text Format (RTF), and HTML. By default, Outlook displays email messages in whatever format they were received.

ℹ️ Check
Verify the policy value for User Configuration >> Administrative Templates >> Microsoft Outlook 2016 >> Outlook Options >> Preferences >> E-mail Options "Read e-mail as plain text" is set to "Enabled". 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 ReadAsPlain is REG_DWORD = 1, this is not a finding.

ℹ️ Check

Verify the policy value for User Configuration >> Administrative Templates >> Microsoft Outlook 2016 >> Outlook Options >> Preferences >> E-mail Options "Read e-mail as plain text" is set to "Enabled". 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 ReadAsPlain is REG_DWORD = 1, this is not a finding.

✔️ Fix
Set the policy value for User Configuration >> Administrative Templates >> Microsoft Outlook 2016 >> Outlook Options >> Preferences >> E-mail Options "Read e-mail as plain text" to "Enabled".