Once you have finished chatting on iMessage, make sure to sign out and show that you are no longer available. Make sure to click on the sign out button on iMessage to indicate that you are no longer available for messaging. If you want to leave iMessage, don't forget to sign out and let others know that you are no longer online. After your conversation on iMessage, remember to sign out to let everyone know that you are offline. Before you leave iMessage, it's essential to click on the sign out option and indicate that you are no longer active. Remember to tap on the sign out button on iMessage and show that you are no longer available for chat. Once you are done with iMessage, be sure to sign out and signify that you have logged off. Make sure to exit iMessage by signing out and demonstrating that you are no longer reachable. If you want to indicate that you are no longer using iMessage, make sure to sign out and show that you have logged off. After finishing your conversation on iMessage, don't forget to click on the sign out option to demonstrate that you are no longer active.

Deregister and Turn Off iMessage Apple Support