Enable throttling for online mail indexing: registry value EnableThrottlingOnlineMailboxes and 1 moreComputerHKLM\SOFTWARE\Policies\Microsoft\Windows\Windows Search

Policy ID: EnableThrottlingOnlineMailboxes
Scope: Computer Configuration
Supported on: Any version of Microsoft Windows with Windows Search 4.0 or later
Source: Administrative Templates (.admx) for Windows 11 2026 Update (26H2) (version 1.0)
Category: Windows Components › Search

When using Microsoft Office Outlook in online mode, you can enable this policy to control how fast online mail is indexed on a Microsoft Exchange server. The lower you set this policy, the lower the burden will be on the corresponding Microsoft Exchange server. The default value for this policy is 120 items per minute. To lower the burden on Microsoft Exchange servers, lower the rate of items indexed per minute. If you disable this policy, then online mail items will be indexed at the speed that the Microsoft Exchange server can support. If you set this policy to not configured, then online mail items will be indexed at the speed of 120 items per minute. This policy has no effect on mail items when using Microsoft Office Outlook in cached mode.

See the full description on the Group Policy page ›

Registry

EnableThrottlingOnlineMailboxes

REG_DWORDComputer

HKLM\SOFTWARE\Policies\Microsoft\Windows\Windows Search Current key

Enabled value: 1
Disabled value: 0

Apply with .reg · CMD · PowerShell

.reg

Windows Registry Editor Version 5.00

[HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows\Windows Search]

; Options (use only one)
; Enabled
"EnableThrottlingOnlineMailboxes"=dword:00000001
; Disabled
"EnableThrottlingOnlineMailboxes"=dword:00000000

CMD

:: Options (use only one)

:: Enabled
reg add "HKLM\SOFTWARE\Policies\Microsoft\Windows\Windows Search" /v "EnableThrottlingOnlineMailboxes" /t REG_DWORD /d 1 /f
:: Disabled
reg add "HKLM\SOFTWARE\Policies\Microsoft\Windows\Windows Search" /v "EnableThrottlingOnlineMailboxes" /t REG_DWORD /d 0 /f

PowerShell

# Common: create the key
New-Item -Path 'HKLM:\SOFTWARE\Policies\Microsoft\Windows\Windows Search' -Force | Out-Null

# Options (use only one)
# Enabled
New-ItemProperty -Path 'HKLM:\SOFTWARE\Policies\Microsoft\Windows\Windows Search' -Name 'EnableThrottlingOnlineMailboxes' -PropertyType DWord -Value 1 -Force | Out-Null
# Disabled
New-ItemProperty -Path 'HKLM:\SOFTWARE\Policies\Microsoft\Windows\Windows Search' -Name 'EnableThrottlingOnlineMailboxes' -PropertyType DWord -Value 0 -Force | Out-Null

EnableThrottlingOnlineMailboxesValue

REG_DWORDComputer

HKLM\SOFTWARE\Policies\Microsoft\Windows\Windows Search Current key

Enabled value: Depends on the option value
Element: Number of items per minute
Value type: REG_DWORD
Minimum value: 6
Maximum value: 600

Apply with .reg · CMD · PowerShell

.reg

Windows Registry Editor Version 5.00

[HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows\Windows Search]

; Value names and types follow the ADMX. Replace <enter value> below with your own data
"EnableThrottlingOnlineMailboxesValue"=dword:<enter value>

CMD

:: Value names and types follow the ADMX. Replace <enter value> below with your own data

reg add "HKLM\SOFTWARE\Policies\Microsoft\Windows\Windows Search" /v "EnableThrottlingOnlineMailboxesValue" /t REG_DWORD /d "<enter value>" /f

PowerShell

# Value names and types follow the ADMX. Replace <enter value> below with your own data

New-Item -Path 'HKLM:\SOFTWARE\Policies\Microsoft\Windows\Windows Search' -Force | Out-Null
New-ItemProperty -Path 'HKLM:\SOFTWARE\Policies\Microsoft\Windows\Windows Search' -Name 'EnableThrottlingOnlineMailboxesValue' -PropertyType DWord -Value '<enter value>' -Force | Out-Null