Make Outlook the default program for E-mail, Contacts, and Calendar: registry value check default clientUserHKCU\software\policies\microsoft\office\16.0\outlook\options\general

Policy ID: L_MakeOutlookthedefaultprogramforEmailContactsandCalendar
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 › Outlook Options › Other

Registry

check default client

REG_DWORDUser

HKCU\software\policies\microsoft\office\16.0\outlook\options\general Current key

Enabled value: 1
Disabled value: 0

Apply with .reg · CMD · PowerShell

.reg

Windows Registry Editor Version 5.00

[HKEY_CURRENT_USER\software\policies\microsoft\office\16.0\outlook\options\general]

; Options (use only one)
; Enabled
"check default client"=dword:00000001
; Disabled
"check default client"=dword:00000000

CMD

:: Options (use only one)

:: Enabled
reg add "HKCU\software\policies\microsoft\office\16.0\outlook\options\general" /v "check default client" /t REG_DWORD /d 1 /f
:: Disabled
reg add "HKCU\software\policies\microsoft\office\16.0\outlook\options\general" /v "check default client" /t REG_DWORD /d 0 /f

PowerShell

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

# Options (use only one)
# Enabled
New-ItemProperty -Path 'HKCU:\software\policies\microsoft\office\16.0\outlook\options\general' -Name 'check default client' -PropertyType DWord -Value 1 -Force | Out-Null
# Disabled
New-ItemProperty -Path 'HKCU:\software\policies\microsoft\office\16.0\outlook\options\general' -Name 'check default client' -PropertyType DWord -Value 0 -Force | Out-Null