We’ve rolled out some improvements to the mailbox screen. Previously these were only available on the beta server.
You can now see which messages have been flagged, and which messages have high or low priorities (as defined by the sender). Currently there is no way for you to set the priority of a message using the web interface - that functionality is planned.
You can change the flag status of a message using the “Mark flagged” or “Mark unflagged” items in the Action menu.
There also some “flag searches” at the top of the messages list, which allow to quickly show only the unread messages, the read messages, or the flagged messages.