Product thumbnail images is main image
Your thumbnail images that you are using in the emails is not the WooCommerce thumbnail image (like you thought), but the main product image. This is very bad news as it will create excessively big loads on disk space.
You can see the it here: https://snag.gy/GT6nDN.jpg
This was an email I just received from an order. As you can see original image is 680x400 (my product image size).
Can you please address this in your next update? Thanks again
Update: I understand now you are using WordPress 'thumbnail' images, rather than the WooCommerce thumbnail images. This explains the issue I am having: https://snag.gy/GT6nDN.jpg
I have set all WordPress image sizes to '0', in order for less image sizes to be created. So your plugin must then be falling back to the main WooCommerce product image, rather than using a thumbnail image.
So I guess what I have to do do is set the product "WordPress" thumbnail image size, in order for my emails to pull in the WordPress thumbnail image rather than the main product image from WooCommerce.