FB have been promising about an‘unsend’ feature for Messenger since seven months ago when Facebook secretly removed some private messages sent by CEO Mark Zuckerberg. An updated preview was released last week.
The new unsend feature, which might come as a big blow to Snapchat, is currently only available for users in Colombia, Poland, Bolivia, and Lithuania; it’s expected to be rolled out to other parts of the world soon.
You can remove a message from recipients’ inboxes within 10 minutes of sending it. After that time limit, you can only delete the message from your inbox, but it will remain in the recipients’ inboxes.
Even after deleting a message, Facebook will retain it for an unspecified amount of time for abuse detection/ NSA monitoring etc.