Use any automation tool like Mailchimp, Zapier or CMS like Wordpress to set up your smart calendar link once and send thousands of reminders automatically.
Create your e-mail or landing page
Go to your e-mail campaign or landing page where you want to place the add-to-calendar button.
Create your smart link
Create your smart link once in my.calendarlink.com - and use the personalization fields of your tool to personalize the link. E.g. use the "appointment date" of your user to automatically generate an event for that specific date.
Copy & paste
Copy & paste the link in your button in your e-mail or website.