By default, the size of the preview thumbnail in Symphony Messaging is set to a maximum height of 256 pixels:
Note: The image could be smaller if the original picture is less than 256 pixels.
If a customer wants to make the preview thumbnail larger, use the min-height variable to set a specific size as desired. To do this, you need to specify in the style attribute the min-height for the img element:
<messageML>
<img style="min-height:350px" src="https://symphony.com/assets/brand/thumb_symphony_shards.jpg"/>
</messageML>
The new code will then render the larger image: