Email clients use different rendering engines to render HTML emails:
Some clients will also add their own styles on top of yours e.g. Gmail sets all
<td> fonts to
font-family: arial,sans-serif;, which could impact how an email renders.
Prior to 2016, all Gmail products stripped out
<link> tags, any CSS inside
<style> tags, and any other CSS that isn’t inlined. In late 2016, Gmail began supporting the
<style> tag and media-queries in most of its products. Here is an update as of 23-Nov-2016: