Configure Outlook object model prompt when accessing an address book
This per-user `REG_DWORD` value controls how Outlook responds when an untrusted program accesses an address book through the Outlook object model.
since 0.9.8.11
Purpose
Show registry keys (1)
HKCU\software\policies\microsoft\office\16.0\outlook\security\promptoomaddressbookaccess
This per-user REG_DWORD value controls how Outlook responds when an untrusted program accesses an address book through the Outlook object model. It applies to address-book entry points protected by the Outlook Object Model Guard.
The supported value data is:
0: Outlook automatically denies the access request.1: Outlook prompts the user to allow or deny access.2: Outlook automatically approves the access request.3: Outlook bases the decision on the Programmatic Access setting in Trust Center, which can take the antivirus status reported by Windows into account.
If the value is absent or the corresponding policy is not configured, the registry value does not impose a specific response. Outlook instead follows the applicable Programmatic Access setting in Trust Center.
Notes
Security
With 0, Outlook blocks the affected calls without asking the user. An untrusted program therefore cannot retrieve address-book data through the protected Outlook object-model entry points.
With 1, the user decides whether the requested access is permitted. If the user grants access for a selected period, that approval applies to every Outlook object-model caller during that period, not only to the program that originally triggered the warning.
With 2, Outlook approves the affected address-book requests from any program without displaying a warning. Malware running in the user's context could consequently retrieve protected address-book information through the Outlook object model. This value does not grant general access to all Outlook data or permission to send messages programmatically; separate protected entry points and policies govern those operations.
With 3, Outlook can suppress warnings for cross-process callers when Windows reports suitable antivirus software in an acceptable state. A change in antivirus status can therefore change whether prompts appear.
Possible side effects
When Outlook automatically denies a request, the object-model call receives no requested data and typically returns MAPI_E_NOT_SUPPORTED. Applications that do not handle this error may stop the current operation or crash.
Prompts produced with value 1 can interrupt unattended automation. A workflow may display multiple warnings when it invokes more than one protected property or method.
Notes
This setting applies only to operations assigned to the Address Book warning category. Reading address information from recipient fields is controlled in part by the separate PromptOOMAddressInformationAccess value.
For Outlook to consume the programmatic security settings from the policy branch, Outlook Security Mode must select Group Policy security settings. This corresponds to AdminSecurityMode set to 3.
Microsoft documentation
Microsoft Learn: Outlook Object Model Security Warnings
Microsoft Learn: Protected Properties and Methods
Microsoft Learn: Microsoft Support and Recovery Assistant indicates an offline scan was forced
Microsoft Download Center: Administrative Template files for Microsoft Office