Microsoft Outlook 2016 Security Technical Implementation Guide

The Microsoft Outlook 2016 Security Technical Implementation Guide (V2 R4) has 64 STIG checks. New to STIG checklists? Read What is a STIG checklist?, CKL vs CKLB, and STIG vs SCAP benchmark.

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Severity

Version

V2 · R4

CurrentPublished Mon Jan 05 2026

Read signed email as plain text must be enforced.

Microsoft Outlook 2016 Security Technical Implementation Guide

Assessment Title

Rule Text

Read signed email as plain text must be enforced.

Description

Discussion Text

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

New to STIG checklists? Read What is a STIG checklist? and CKL vs CKLB.

Objective

V-251865

Rule

SV-251865r961863_rule

Severity

medium

Rule Version

DTOO215

Documentable

false

IA Controls

NIST SP 800-53

Rev 5

Assessment Procedure

Check Text

Verify the policy value for User Configuration >> Administrative Templates >> Microsoft Outlook 2016 >> Outlook Options >> Preferences >> E-mail Options "Read signed 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 ReadSignedAsPlain is REG_DWORD = 1, this is not a finding.

Implementation Procedure

Fix Text

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

STIG check 60 of 64 in the Microsoft Outlook 2016 STIG checklist

← Previous · V-251863Read EMail as plain text must be enforced.Next · V-251866 →The default message format must be set to use Plain Text.