Xangle Camera Server allows you to use a custom HTML template for emails sharing.
You can specify which HTML template file you want to use in the "Apps settings" tab.
You can download an example of a basic HTML email right here
All urls from this file must be accessible from the internet. If you don't have a web server to host your logo, you can use a free pictures hosting provider such as imgur.com (be careful to add the complete image URL, ending by .png or .jpg).