If the 24 hour Trip Reminder is enabled on your account, the Trip Reminder alert is special type of scheduled alert that does not require the traveler to opt-in to alerting, so any trip that has the traveler's email address included will receive a Trip Reminder alert 24 hours prior to their published gate departure time. If the traveler is Opted-in, they will receive Traveler Trip Alerts.
If the traveler wants to opt out of all alerting, including the Trip Reminders alerts, first you can search for their Traveler Profile.
Trip Center - Traveler Profile Search:
Then toggle the Activate Alert function to Off in their Traveler Profile and click Save.
Alternatively, if the traveler wishes to opt out of alerting themselves, they can log into their own Traveler Profile and toggle the Activate Alert function to Off and click Save:
To enable or disable Trip Reminders: