Do not allow an OST file to be created: registry value noostUserHKCU\software\policies\microsoft\office\16.0\outlook\ost

Policy ID: L_OSTCreation
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 › Account Settings › Exchange

Registry

noost

REG_DWORDUser

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

Enabled value: 2
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\ost]

; Options (use only one)
; Enabled
"noost"=dword:00000002
; Disabled
"noost"=dword:00000000

CMD

:: Options (use only one)

:: Enabled
reg add "HKCU\software\policies\microsoft\office\16.0\outlook\ost" /v "noost" /t REG_DWORD /d 2 /f
:: Disabled
reg add "HKCU\software\policies\microsoft\office\16.0\outlook\ost" /v "noost" /t REG_DWORD /d 0 /f

PowerShell

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

# Options (use only one)
# Enabled
New-ItemProperty -Path 'HKCU:\software\policies\microsoft\office\16.0\outlook\ost' -Name 'noost' -PropertyType DWord -Value 2 -Force | Out-Null
# Disabled
New-ItemProperty -Path 'HKCU:\software\policies\microsoft\office\16.0\outlook\ost' -Name 'noost' -PropertyType DWord -Value 0 -Force | Out-Null