Change the limit for the number of MIME headers: registry value mimeheadersUserHKCU\software\policies\microsoft\office\16.0\outlook\options\mail

Policy ID: L_ChangethelimitMIMEheaders
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 › MIME to MAPI Conversion

Registry

mimeheaders

REG_DWORDUser

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

Enabled value: Depends on the option value
Element: -
Value type: REG_DWORD
Maximum value: 99999

Apply with .reg · CMD · PowerShell

.reg

Windows Registry Editor Version 5.00

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

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

CMD

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

reg add "HKCU\software\policies\microsoft\office\16.0\outlook\options\mail" /v "mimeheaders" /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 'HKCU:\software\policies\microsoft\office\16.0\outlook\options\mail' -Force | Out-Null
New-ItemProperty -Path 'HKCU:\software\policies\microsoft\office\16.0\outlook\options\mail' -Name 'mimeheaders' -PropertyType DWord -Value '<enter value>' -Force | Out-Null