Zscaler alerting is not limited to email. Alert Rules and detection/response notifications can be sent through webhooks or integrated with collaboration, ITSM, UCaaS, and other third-party tools depending on configuration. Option D (In addition to email, notifications, based on Alert Rules, can be shared with leading ITSM or UCAAS tools over Webhooks) is correct because email and webhook-based integrations support external notification workflows.
Why the other options are incorrect:
A). Email is the only method for notifications as that is universally applicable and no other way of sending them makes sense: Email and webhooks forward alerts to people or third-party systems for response workflows.
B). In addition to email, text messages can be sent directly to one cell phone to alert the CISO who is then coordinating the work on the incident: Email and webhooks forward alerts to people or third-party systems for response workflows.
C). Leading ITSM systems can be connected to the Zero Trust Exchange using a NSS server, which will then connect to ITSM tools and forwards the alert: NSS is for log streaming to analytics/SIEM destinations. Alert-rule notifications use email and webhook integrations, including ITSM or UCaaS tools.