I always view my emails as plain text in Thunderbird, mostly because I think HTML email is a pox upon the earth. As a result of that, I tend to see typos that people don’t normally notice. Note for example this email from J. Crew:
J. Crew plain-text email copy
No capitalization on the first letter, time spelled as “tiem”, and don’t forget free HIPPING. I’m not sure what that is, but it sounds kind of painful. At least it’s free though, right? Right.