Custom Outlook Object Model (OOM) action execution prompts must be configured.

Custom actions add functionality to Outlook that can be triggered as part of a rule. Among other possible features, custom actions can be created that reply to messages in ways that circumvent the Outlook model's programmatic send protections. By default, when Outlook or another program initiates a custom action using the Outlook object model, users are prompted to allow or reject the action. If this configuration is changed, malicious code can use the Outlook object model to compromise sensitive information or otherwise cause data and computing resources to be at risk.