Message text not showing when receiving a contact form e-mail from calderra form

When a client receives a message from a customer who has filled out the contact form on his site, he receives a notification e-mail but there the actual text body of the message isn’t showing, calderra forms is the plugin that is being used. Does anybody have an idea why this might be? The plugin is up to date, although a new version of wordpress is available that hasn’t been updated..