List of allowed HTML tags and their attributes:

• a: href, title, name, style, id, class, shape, coords, alt, target.
• b: style, id, class.
• br: style, id, class.
• big: style, id, class.
• blockquote: title, style, id, class.
• caption: style, id, class.
• code: style, id, class.
• del: title, style, id, class.
• div: title, style, id, class, align.
• dt: style, id, class.
• dd: style, id, class.
• font: color, size, face, style, id, class.
• h1: style, id, class, align.
• h2: style, id, class, align.
• h3: style, id, class, align.
• h4: style, id, class, align.
• h5: style, id, class, align.
• h6: style, id, class, align.
• hr: style, id, class.
• i: style, id, class.
• img: style, id, class, src, alt, height, width, title.
• ins: title, style, id, class.
• li: style, id, class.
• map: shape, coords, href, alt, title, style, id, class, name.
• ol: style, id, class.
• p: style, id, class, align.
• pre: style, id, class.
• s: style, id, class.
• small: style, id, class.
• strong: style, id, class.
• span: title, style, id, class, align.
• sub: style, id, class.
• sup: style, id, class.
• table: border, width, style, id, class, cellspacing, cellpadding.
• tbody: align, valign, style, id, class.
• td: width, height, style, id, class, align, valign, colspan, rowspan.
• tfoot: align, valign, style, id, class, align, valign.
• th: width, height, style, id, class, colspan, rowspan.
• thead: align, valign, style, id, class.
• tr: align, valign, style, id, class.
• u: style, id, class.
• ul: style, id, class.
• php: id.
• html: xmlns.
• head
• body
• meta: content, name, http-equiv.
• title
• style: type.
• link: type, rel, href.

Unsupported tags are automatically cut by the system for security reasons.

Can I Email is an incredible resource for researching specific HTML or CSS email features, but it can be time-consuming.