We have a chain of delivery that is meant to ensure (as much as possible) that emails are delivered. When an email is sent, we attempt to send through a service called Postmark, they are the leading email sending service in the industry. If they are unable to deliver the email, then we fall back to Sendgrid which is another leading email deliverer.
Then if that fails we will try back to sending the email using our own server which almost never happens. In addition to the services we use to deliver, our email template is simple and optimized to satisfy the majority of spam filters.