Webmail considers messages that you have opened as having been read. Conversations containing unread messages are shown in bold. You can also mark unread mail as read.
You can change a message's status back from read to unread by right-clicking on the message and choosing Mark as Read from the menu that appears. You can also mark a conversation as unread.
Marking a conversation as unread marks all messages within that conversation as unread.
Marking a single message as unread marks the conversation that contains the message unread.
You can mark emails as unread by selecting the email you wish to mark by clicking in the check box. Then select "Mark as Unread" from the "More Actions..." drop down box.
You can change the status of an email in Webmail Mobile by first opening the email you wish to change. Then you can change the email to show as unread from the drop down menu "More Actions..." at the bottom of the screen.