When a standard segment is created, it is automatically populated with three topics that should not be deleted.
All Topics - "All Topics" is the initial root parent of the topic tree for the segment. It is named all topics because when viewed from the Find Answers page with "Include All Sub-topics" selected, the articles from all topics within the segment are displayed. But it can be renamed as desired to reflect how you intend to configure iService (e.g., Other Questions).
_SPAM - The spam topic is used to separate spam messages and improve the accuracy of reports. The Message Queue - SPAM button will automatically change the topic of the message to _SPAM, and therefore this topic should not be removed. In addition to the SPAM button, you can create filters to identify messages that are spam and move them to this topic.
_Undeliverable - This topic is used to route bounced messages that do not require a response. It is typically used with a set of bounce filters that will identify undeliverable notices and move them into this topic.