You can manage messages in bulk from the Message Center. Click the bubble next to each message you want to manage, or click the bubble at the top of the column to select all messages. You can then use the thin ribbon at the top of the message center, just beneath +Create Message, to do one of the following:
Mark all as read: Click this button to mark all selected messages as read.
Mark all as unread: Click this button to mark all selected messages as unread.
Delete: Click this button to delete all selected messages.