This is all very nice, but the fact that the article doesn't even _mention_ images or attachments shows how divorced it is from the reality of most people's email experience. I happily used emacs as my mail-reader from 1989 to about 2009 (first RMAIL mode, then VM). The increasing importance of non-text formats made it cumbersome, and I somewhat reluctantly switched to GMail. It's hard to imagine switching back now.
I am a researcher, and when my colleagues want to discuss results they have the nasty habit of sending plots and documents as email attachments. My most important emails have PDF documents or plots attached, with the email text commenting the attachment itself. The problem with mutt is that it allows you to start helper supporting application to open attachments, but it waits for the application to finish before returning to the email text. This is not what I want, for I obviously have to read the email and view the attachment at the same time!
The usual trick here is to fire the application in background (using "&"), so that mutt can resume operations immediately after the helper application has started. The problem is that once mutt resumes, it removes the temporary file containing the attachment, so if the helper application starts slowly it might not find it. One can force mutt to wait some seconds after having launched the helper application, but this not helps if the attachment is a multi-page PDF file, because once the wait has expired, the PDF file disappears and is no longer browsable.
I must say that using mutt was an enlightening experience (email browsing can be fast, after all!), but thunderbird makes me far more productive.