Savoir si un email envoyé a été ouvert

Yes, with a read receipt, but it depends on the recipient's willingness to activate it and to confirm that they have read it.

In practice, it’s useless. The way to ensure that the content has been read is to put the essential part of an email for download on a site like https://www.transfernow.net/, and then create a link by checking the download confirmation options.

There are also specialized services like Streak: https://www.streak.com/

Another way to ensure a message is read is to send it via an app like Whatsapp or Messenger.