I got it working with the combination of keys below and NEITHER Outlook nor Sage50 being set to "Run as administrator"
This is for Office 365 Outlook 2016 CLICK-to-RUN version - 32 bit Office running on 64-bit Windows 10 v.1809

There's a MS KB article 3189806 about the ObjectModelGuard that is recently updated to cover up to Outlook 2019, and how to tell if your Office is MSI or Click-to-Run -    support.microsoft.com/.../3189806

Windows Registry Editor Version 5.00

[HKEY_LOCAL_MACHINE\SOFTWARE\WOW6432Node\Microsoft\WindowsMessagingSubsystem]
"MAPI"="1"

[HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook\Security]
"AdminSecurityMode"=dword:00000003
"PromptSimpleMAPISend"=dword:00000002

[HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\16.0\Outlook\Security]
"AdminSecurityMode"=dword:00000003
"PromptOOMSend"=dword:00000002
"promptoomaddressinformationaccess"=dword:00000002
"promptoomaddressbookaccess"=dword:00000002
"PromptSimpleMAPISend"=dword:00000002
"PromptSimpleMAPINameResolve"=dword:00000002
"PromptSimpleMAPIOpenMessage"=dword:00000002

[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Office\16.0\Outlook\Security]
"ObjectModelGuard"=dword:00000002

[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Office\ClickToRun\REGISTRY\MACHINE\Software\Wow6432Node\Microsoft\Office\16.0\Outlook\Security]
"ObjectModelGuard"=dword:00000002

[HKEY_LOCAL_MACHINE\SOFTWARE\WOW6432Node\Microsoft\Office\16.0\Outlook\Security]
"ObjectModelGuard"=dword:00000002