A playbook needs to dynamically add an email sender's address to a Cortex XSOAR list...

XSOAR’s built-inLists Servicesupports operations such as creating, updating, and appending items to lists using automation commands. The correct command for appending a value to an existing list is!addToList, which inserts the new string (in this case an email address) into the list array stored within the XSOAR Lists infrastructure.

The Admin Guide describes!addToListas the intended mechanism to add new elements to a named list while automatically handling JSON structure and avoiding duplication errors.

Option B, !appendToListContext, modifiescontext data, not persistent platform lists—therefore it will not update the BlockedSenders list. Option C misuses !setIncident, which updates incident fields only, not system lists. Option D, !createListItem, is used when an integration or automation script exposes a “create item” action, not for native XSOAR lists.

Thus, the correct and documented method of adding an email value to a persistent XSOAR list is!addToList, making optionAthe accurate choice.