Sending secure email is one of the questions we hear more and more. This is a result of an increasing number of email security risks, hacks and other threats. So you're not the only person wondering, "How to send secure email in Gmail? (or any other public email service for that matter?") You'll find the answer in this article. This article concludes with a link to a free encrypted email service First check whether you meet the conditions.

But more so, external style cannot be applied to a subsection of a web page unless they force it into an iframe, which has all sorts of issues of it's own which is why external CSS is usually ignored. Inline CSS is often stripped by the tag strippers who don't want you turning things on or off... and media queries shouldn't even play into it since the layout should be controlled by the page it's being shown inside (for webmail) or the client itself, NOT your mail.

Also cross-compatibility with mail clients can be hairy, so you should see what the industry experts are doing.