Among the post, this article[0] is referenced, which does mention testing on outlook and is more technical! It might be it.
> It turns out that all email services take your original message and conveniently wrap it in a div (with a class) or a blockquote, meaning you can use that as a CSS selector. It's so stupidly simple.
I wonder how the situation evolved from a decade ago. Time to do a bit of research!
0: https://web.archive.org/web/20160903225343/http://jonathan-k...
