That option has been taking out since quite a while. There are several reasons: learner has full control over his mail client, you can never have a foolproof result. It can be done with JS but the learner will be able to edit everything.
You can use an internal server to replace a LMS. Or insert an automatically created certificate and ask the learner to sent a screenshot of that certificate? Still... not completely foolproof since logically it is up to the learner.