They're there to show you what messages you've replied to (backwards arrow), what messages you've forwarded (forward arrow), and what messages you've flagged for follow-up.

If you reply to and forward the same message, Yahoo!7 Mail shows you the icon of what you did most recently. If you forward a message, Yahoo!7 Mail puts the forward arrow icon next to it. If, later, you reply to the same message, Yahoo!7 Mail displays the backward arrow icon.

You can also flag a message to follow up on later. Here's how:

1. Click the message you'd like to flag.
2. Find the "More Actions" button above the main Yahoo!7 Mail window.
3. Click it and select "Flag for Follow-up."

Now look for the flag icon next to the message. It's to the right of the other columns.