Autoplay video in email refers to the technical option by which an embedded video starts to play as soon as the message is displayed in inboxes.
Autoplay activation is theoretically used to maximize chances of the video being played but it raises several issues additionnal to usual rendering and deliverability issues.
autoplay may be seen as a disturbance in particular with sounds and for adwork opening.
autoplay consumes bandwidth.
autoplay can consumes bandwidth at the recipient expenses when the email is opened on smartphones.
For these reasons, video emails are most often offered as static image with a "click to play" button.