I'm the author of the article. All the other web mail clients from Yahoo! Mail, Outlook.com, Comcast and so forth support the style tag. If it was a big securit

I'm the author of the article. All the other web mail clients from Yahoo! Mail, Outlook.com, Comcast and so forth support the style tag. If it was a big security attack vector, all those clients wouldn't be doing that. The other webmails rewrite ids and classes and prepend unique identifiers to prevent them from clashing with their own namespace (AOL is the only one that puts it in an iframe). Interestingly Gmail webmail actually supports the style tag but strips out id and class selectors in them leaving element selectors - so they're actually doing some heavy duty parsing already. As for it being an inherently text medium. I would say it depends on the recipient. Emails do not need to be web pages, but simple CSS styling can go a long way to ease readability in emails - especially in a long curated newsletter like Product Hunt.