In the mid 2000s I had a job building html marketing emails (legal "spam" basically). The main targets were enterprise tech managers. I quickly found out that we could double the click rate on the emails by including a plain text version (Lotus Notes email client was still a thing and many tech people had it set to read only the plain text mime part of emails).
Clients were scepticall at first because they wanted to make sure that the user was seeing all the visual branding in the html+images. To convince them, I started using gamefaq style ASCII typography tricks to make a visual representation of the layout. It worked great.