Only connect if Proxy Server certificate has this principal name: registry value proxyserverprincipalnameUserHKCU\software\policies\microsoft\office\16.0\outlook\rpc

Policy ID: L_RPCProxyServerPrincipalName
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

proxyserverprincipalname

REG_EXPAND_SZUser

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

Enabled value: Depends on the option value
Element: Specify the proxy server principal name (see Explain tab for details):
Value type: REG_EXPAND_SZ
Required: true
Expandable string (REG_EXPAND_SZ): true

Apply with .reg · CMD · PowerShell

.reg

Windows Registry Editor Version 5.00

[HKEY_CURRENT_USER\software\policies\microsoft\office\16.0\outlook\rpc]

; Value names and types follow the ADMX. Replace <enter value> below with your own data
; hex(2) and hex(7) data must be written as hexadecimal (UTF-16LE)
"proxyserverprincipalname"=hex(2):<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\rpc" /v "proxyserverprincipalname" /t REG_EXPAND_SZ /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\rpc' -Force | Out-Null
New-ItemProperty -Path 'HKCU:\software\policies\microsoft\office\16.0\outlook\rpc' -Name 'proxyserverprincipalname' -PropertyType ExpandString -Value '<enter value>' -Force | Out-Null