I've read of issues with the way that gmail handles HTML emails. That said, this plugin makes no change in the way that an email is "presented" to an email viewer like gmail.

The primary change that this plugin introduces is moving the CSS styling specifications from each HTML email template to a separate file, allowing that single file to be updated with all styling needed for all emails. That CSS file's contents are then read and placed into a <style> tag in the email's header (kind of like using an @import statement to pull an additional CSS).

Just like the built-in Zen Cart's HTML emails, there is no in-line styling on the HTML tags other than the specification of a class= attribute that references a collection of styles to be applied.