By default, when you arrange messages by conversation topic, only unread messages are displayed. To see all the messages, click the arrow next to the conversation title (circled above).
There's nothing more frustrating than coming back to an Inbox full of messages all about the same thing. Well, maybe one thing is worse…that's when you start reading somewhere in the middle of the conversation, respond, and then discover later that three other people gave the same response—and it turned out to be wrong.
When you arrange messages by conversation, you can leave your Inbox with confidence, knowing that you can avoid this type of embarrassment.
At first, you'll see only the bits of the conversation that you haven't yet read. Wondering how you can see the whole conversation? The picture on the left shows where you can click to see all of the messages.