Gmail's HTML Tag Whitelist
There are various sites that list which CSS properties Gmail supports. However, I could not find one that lists which HTML tags its whitelist filter allows. This is relevant because Gmail has limited support for selectors, and specifically only element names may be used. Being able to use more tags is therefore helpful in making selectors more sane.
This list was determined by sending an HTML email with all HTML elements and seeing which came through.
Supported HTML Tags
<a>
<abbr>
<acronym>
<address>
<area>
<b>
<bdo>
<big>
<blockquote>
<br>
<button>
<caption>
<center>
<cite>
<code>
<col>
<colgroup>
<dd>
<del>
<dfn>
<dir>
<div>
<dl>
<dt>
<em>
<fieldset>
<font>
<form>
<h1>
<h2>
<h3>
<h4>
<h5>
<h6>
<hr>
<i>
<img>
<input>
<ins>
<kbd>
<label>
<legend>
<li>
<map>
<menu>
<ol>
<optgroup>
<option>
<p>
<pre>
<q>
<s>
<samp>
<select>
<small>
<span>
<strike>
<strong>
<sub>
<sup>
<table>
<tbody>
<td>
<textarea>
<tfoot>
<th>
<thead>
<u>
<tr>
<tt>
<u>
<ul>
<var>
Unsupported HTML tags
<applet>
<article>
<aside>
<audio>
<base>
<basefont>
<bdi>
<bgsound>
<blink>
<body>
<canvas>
<content>
<data>
<datalist>
<decorator>
<details>
<dialog>
<element>
<embed>
<figcaption>
<figure>
<footer>
<frame>
<frameset>
<head>
<header>
<hgroup>
<html>
<iframe>
<isindex>
<keygen>
<link>
<listing>
<main>
<mark>
<marquee>
<menuitem>
<meta>
<meter>
<nav>
<nobr>
<noframes>
<noscript>
<object>
<output>
<param>
<picture>
<progress>
<rp>
<rt>
<ruby>
<script>
<section>
<shadow>
<source>
<spacer>
<style>
<summary>
<template>
<time>
<title>
<track>
<video>
<wbr>
<xmp>