You can use folders to organize your messages in the Messages tab. Folders can be nested inside other folders. Here's how to create a new folder:
- Choose Message > New Message Folder from the menu bar at the top of your screen
- You can also create a folder by clicking the popup arrow next to the New Message button in the toolbar and choosing "New Message Folder"
To move a message into a folder, drag the message from the list of messages and drop it onto the icon for your newly-created folder.
You can select multiple messages by holding down the shift key (for contiguous selection) or command key (for non-contiguous selection) on your keyboard and clicking the messages.