我如何可以完全个性化电子邮件的外观?

This is interesting, I’ve seen this, I’ve found some ancient posts related to this:

How to change the style of the email template of the digest? - dev - Discourse Meta

Example Plugin: Custom Activity Summary Template - plugin - Discourse Meta

A more recent one: How to show Full Name in Embeds - dev - Discourse Meta may be able to help me get the desired effect, I will try this later and I will let everybody know how I get along.