Please have a look at https://useplaintext.email/
Why is plaintext better than HTML?
HTML emails are mainly used for marketing - that is, emails you probably don’t want to see in the first place. The few advantages they offer for end-users, such as links, inline images, and bold or italic text, aren’t worth the trade-off.
Privacy invasion and tracking
Virtually all HTML emails sent by marketers include identifiers in links and inline images which are designed to extract information about you and send it back to the sender. Examine the URLs closely - the strange numbers and letters are unique to you and used to identify you. This information is used to hack your brain, attempting to find advertisements which are more likely to influence your buying habits. HTML emails are good for marketers and bad for you.