As you probably know, you can host webinar using Teams.
Well, Teams webinars are now sending reminders to participants about 1 hour before the event starts.
In addition of the introduction of reminders, if you have Teams Premium licenses organizers will be able to edit the content of the reminder email as well as the time to send it.
There is no action nor administrator control to manage this feature.
Below is a sample of the reminder email; it includes the custom theme details