To view a slideshow of pictures in an email message instead of scrolling through them individually, click the Slideshow button to have Mail display the photos full screen, one at a time. You can also use the Slideshow controls to display all the pictures at once and click another button to send your favorites directly to iPhoto.
Related: Apple mail, sending pictures, Viewing all inboxes in the new Mail, Mail cannot send message using server, How Do I Use the Merge/mail Feature for a Mass E-mail?, Mail Message Focus.
