How do I find out who sent me a registered letter?

To find out who sent you a registered letter, you can check the tracking number provided by the postal service, which may give you details about the sender. If you have the letter in hand, look for any identifying information on the envelope or inside the letter. Additionally, you can contact the postal service for assistance, as they may have more information about the sender. If all else fails, the sender's details may be disclosed upon delivery confirmation.