Animation can bring your audiences' user experience to the next level. The simplest way to achieve this in HTML email is through an animated GIF. Embed a gif file in exactly the same way you do an image file. Coverage of GIFs is generally good, but its worth mentioning the email clients that don't support GIF animation. Instead of playing the animation they will only show the first frame of the sequence, so be sure to place all important content on this frame.
Email clients without animated GIF support:
Outlook 2007, 2010 and 2013