Using the Read New Mail Button

  Clicking on the Read New Mail button adds new messages
  to the INBOX folder and displays the new message in the
  current Read window.

  You cannot read new mail if you are reading a message from
  the INBOX in a Read window other than the default Read
  window or if you are replying to a message in the INBOX
  folder.

  Additional topics:

  *   Using a Read Window