Trust logic for file attachments: registry value UseTrustedHandlersUserHKCU\Software\Microsoft\Windows\CurrentVersion\Policies\Attachments

Policy ID: AM_EstimateFileHandlerRisk
Scope: User Configuration
Supported on: At least Windows XP Professional with SP2
Source: Administrative Templates (.admx) for Windows 11 2026 Update (26H2) (version 1.0)
Category: Windows Components › Attachment Manager

Registry

UseTrustedHandlers

REG_DWORDUser

HKCU\Software\Microsoft\Windows\CurrentVersion\Policies\Attachments Current key

Enabled value: Depends on the option value
Element: Determine risk by

Options
Item	Stored value
Preferring the file handler	2
Looking at the file handler and type	3
Preferring the file type	1

Apply with .reg · CMD · PowerShell

.reg

Windows Registry Editor Version 5.00

[HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies\Attachments]

; Options (use only one)
; Preferring the file handler
"UseTrustedHandlers"=dword:00000002
; Looking at the file handler and type
"UseTrustedHandlers"=dword:00000003
; Preferring the file type
"UseTrustedHandlers"=dword:00000001

CMD

:: Options (use only one)

:: Preferring the file handler
reg add "HKCU\Software\Microsoft\Windows\CurrentVersion\Policies\Attachments" /v "UseTrustedHandlers" /t REG_DWORD /d 2 /f
:: Looking at the file handler and type
reg add "HKCU\Software\Microsoft\Windows\CurrentVersion\Policies\Attachments" /v "UseTrustedHandlers" /t REG_DWORD /d 3 /f
:: Preferring the file type
reg add "HKCU\Software\Microsoft\Windows\CurrentVersion\Policies\Attachments" /v "UseTrustedHandlers" /t REG_DWORD /d 1 /f

PowerShell

# Common: create the key
New-Item -Path 'HKCU:\Software\Microsoft\Windows\CurrentVersion\Policies\Attachments' -Force | Out-Null

# Options (use only one)
# Preferring the file handler
New-ItemProperty -Path 'HKCU:\Software\Microsoft\Windows\CurrentVersion\Policies\Attachments' -Name 'UseTrustedHandlers' -PropertyType DWord -Value 2 -Force | Out-Null
# Looking at the file handler and type
New-ItemProperty -Path 'HKCU:\Software\Microsoft\Windows\CurrentVersion\Policies\Attachments' -Name 'UseTrustedHandlers' -PropertyType DWord -Value 3 -Force | Out-Null
# Preferring the file type
New-ItemProperty -Path 'HKCU:\Software\Microsoft\Windows\CurrentVersion\Policies\Attachments' -Name 'UseTrustedHandlers' -PropertyType DWord -Value 1 -Force | Out-Null