User blog comment:Kirkburn/Technical Update: April 13, 2015/@comment-1341868-20150428005919/@comment-452-20150429001220

I think I might know what the problem is: they're not sending "plain-text" emails, they've fixed their multipart emails so that the text/plain portion is no longer blank.

So, to see the text/plain email, you need to change your email client's settings to show you text/plain emails only. If you're using a webmail service, that may not actually be possible to do by default.

edit: BTW, comments about this should probably go on User blog:Kirkburn/Technical Update: April 27, 2015, since that's the new blog post talking about it.