Evolution compresses the To, Cc and Bcc headers of received mail and shows only five addresses in the message preview.

To see all recipients, click the icon next to the To: or Cc: line, or click the ellipsis (…) at the end of the five displayed addresses.

To collapse all of the message headers and just display the subject and sender in one line, click the icon next to the From: line. This is helpful on small screens.