AutoDiscover

As of 2024-11-16, the content of this page was moved into the Gromox manpage autodiscover(7) and our KB page on Outlook.

M365 authentication dialog

When a DNS zone is M365-enabled (DNS TXT record on the domain with contents like MS=ms12345678), Outlook will present a mini browser window for M365 authentication. This can be permanently disabled by setting ExcludeExplicitO365Endpoint:

[HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook\AutoDiscover]
"EnableOffice365ConfigService"=dword:00000000
"ExcludeExplicitO365Endpoint"=dword:00000001

[HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\16.0\Outlook\AutoDiscover]
"EnableOffice365ConfigService"=dword:00000000
"ExcludeExplicitO365Endpoint"=dword:00000001

EnableOffice365ConfigService

In Outlook versions before 16.0.9327.1000, this URL was used to automatically provision O365 endpoints, overriding some AutoDiscover behavior
ExcludeExplicitO365Endpoint

In Outlook 2016+ (versions after 16.0.6741.2017), this configuration parameter is used to proxy AutoDiscover requests via Microsoft servers. Usage of this service is possible

# with grommunio if the AutoDiscover entries have been configured, and/or # when globally resolvable records are pointing to grommunio as the endpoint.

For configuration via Group Policy, ADMX templates can be found at https://www.microsoft.com/en-us/download/details.aspx?id=49030.