How Do I Create and Use Labels?
Only you can see your labels, so whether you mark a message with "The Best Listings," "Maybe Next Year," or "Homes with a Swimming Pool," the sender will never know.
Once you have created a label you can apply it to any conversation. From the left sidebar in your Messaging System you can access all of your labels. By clicking on the label name you can view all of the conversations that have the selected label applied to them.