Unread E-Mails are marked with the Unread icon . In order to mark an E-Mail as read or unread, you can do the following:
mark an individual E-Mail or a complete E-Mail conversation as read or unread
mark all E-Mails of an E-Mail folder as unread
How to mark an E-Mail as unread:
Select a read E-Mail.
Click on More in the toolbar. Click on Mark as unread in the menu.
In order to mark this E-Mail as read, click on Mark as read.
Tip: You can also mark multiple E-Mails at once as unread.
How to mark all E-Mails of a folder as read:
Select an E-Mail folder in the folder tree.
Click the Folder-specific actions icon next to the folder name. Click on Mark all E-Mails as read.