Signature Warning: registry value warnaboutinvalidUserHKCU\software\policies\microsoft\office\16.0\outlook\security

Policy ID: L_SignatureWarning
Scope: User Configuration
Supported on: At least Windows Server 2008 R2 or Windows 7
Source: Microsoft 365 Apps / Office Administrative Templates (version 5568.1000)
Category: Microsoft Outlook 2016 › Security › Cryptography

Registry

warnaboutinvalid

REG_DWORDUser

HKCU\software\policies\microsoft\office\16.0\outlook\security Current key

Enabled value: Depends on the option value
Element: Signature Warning

Options
Item	Stored value
Let user decide if they want to be warned	0
Always warn about invalid signatures	1
Never warn about invalid signatures	2

Apply with .reg · CMD · PowerShell

.reg

Windows Registry Editor Version 5.00

[HKEY_CURRENT_USER\software\policies\microsoft\office\16.0\outlook\security]

; Options (use only one)
; Let user decide if they want to be warned
"warnaboutinvalid"=dword:00000000
; Always warn about invalid signatures
"warnaboutinvalid"=dword:00000001
; Never warn about invalid signatures
"warnaboutinvalid"=dword:00000002

CMD

:: Options (use only one)

:: Let user decide if they want to be warned
reg add "HKCU\software\policies\microsoft\office\16.0\outlook\security" /v "warnaboutinvalid" /t REG_DWORD /d 0 /f
:: Always warn about invalid signatures
reg add "HKCU\software\policies\microsoft\office\16.0\outlook\security" /v "warnaboutinvalid" /t REG_DWORD /d 1 /f
:: Never warn about invalid signatures
reg add "HKCU\software\policies\microsoft\office\16.0\outlook\security" /v "warnaboutinvalid" /t REG_DWORD /d 2 /f

PowerShell

# Common: create the key
New-Item -Path 'HKCU:\software\policies\microsoft\office\16.0\outlook\security' -Force | Out-Null

# Options (use only one)
# Let user decide if they want to be warned
New-ItemProperty -Path 'HKCU:\software\policies\microsoft\office\16.0\outlook\security' -Name 'warnaboutinvalid' -PropertyType DWord -Value 0 -Force | Out-Null
# Always warn about invalid signatures
New-ItemProperty -Path 'HKCU:\software\policies\microsoft\office\16.0\outlook\security' -Name 'warnaboutinvalid' -PropertyType DWord -Value 1 -Force | Out-Null
# Never warn about invalid signatures
New-ItemProperty -Path 'HKCU:\software\policies\microsoft\office\16.0\outlook\security' -Name 'warnaboutinvalid' -PropertyType DWord -Value 2 -Force | Out-Null