https://www.cnet.com/news/facebook-will-let-you-unsend-messages-after-being-caught-deleting-zuckerbergs/

In the future, you'll be able to delete your messages from other peoples' inboxes.

Messages sent from Zuckerberg were discovered to disappear after a certain length of time. While Facebook says it instituted the policy for security reasons, the fact that the company never revealed its actions is another sign that Facebook hasn't been completely honest with its more than 2 billion monthly users.