Twilio SendGrid posts the Delivered event after the destination server accepts the message with a
250 OK response. Once an email is accepted by the destination server, we are unable to see what happens to the message. The receiving server could send it to the inbox, queue it for later delivery, put it into the spam folder, etc.
Often times, a recipient domain will initially accept a message for delivery, and then apply additional filtering afterwards. In this situation, we would have posted the Delivered event, but not have any insight into the additional filtering. Any additional Twilio SendGrid events for your email message would be triggered by recipient engagement (i.e. open/click events, unsubscribes, etc.).