This is one of the riders with his horse in a Pony Express reenactment. You can see the mailbags on the horse.  There are four locked pouches full of mail.
<a rel="nofollow" class="external text" href="https://www.flickr.com/people/17578215@N00">Brett Neilson</a>
CC BY 2.0
<a href="//commons.wikimedia.org/wiki/Flickr" class="mw-redirect" title="Flickr">Flickr</a>: <a rel="nofollow" class="external text" href="https://www.flickr.com/photos/17578215@N00/573254951">Pony Express Re-Ride</a>