There are three ways to mark all emails in a folder as read.

Method 1:

1. Click the More icon at the top-right corner of the email list.
2. Select Mark Folder as Read in the drop-down menu.
   

Method 2:

1. Right-click on the folder you would like to mark as read.
2. Select Mark Folder as Read from the drop-down menu.
   

Method 3:

1. Select an email from the email list.
2. In the top-left corner of the email list, click the check box  icon.
3. Click on Select all mails in this folder.
4. Click More in the email detail view panel.
5. Select Mark as Read, in the drop-down menu.