There are often issues with email templates that cause a UI bug on specific email clients (e.g. outlook)
mjml.io is a framework that makes responsive emails easy. MJML XML-like markup language that will be parsed to email client-friendly HTML.
Why? As there is no standard for email clients to display HTML emails every client uses its own rendering engine. While this should not be a problem in the modern world, it actually is, because most clients only support obsolete or legacy HTML, a limited amount of CSS rules, and more to consider. So if you don't want to write table structures bigger than your actual project, MJML is your way to go as it's doing this for you.
How does it look like? https://mjml.io/try-it-live/templates/austin
How to implement this in Java? https://ditsche.dev/blog/mjml-emails-with-spring-boot