What are the options for displaying a mailbox?
The Mail Preferences option in the settings (gear icon) in Horde menu lets you customize the preferences for Mail and Mailbox Display.
With Mailbox Display Preferences submenu, you can set the mail sorting criteria, messages per page, etc. according to your needs.
If you see an unread mail at the top, instead of new mails, you should select First Page from the options in the When opening a mailbox for the first time, where do you want to start? box.