Anniversary reminders are sent to the second cousins (and closer) of the couple who are celebrating their wedding anniversary. These reminders are sent out automatically once the marriage event has been updated with the proper date, etc.
Like birthday reminders, these reminders are also sent both seven days before the anniversary and on the anniversary itself. The reminder includes a link to add a special greeting which will be delivered to the person’s profile on their anniversary. If you post the greeting prior to the anniversary date, it may be kept and sent on the day of the anniversary itself.