Suppted html content by mail client like gmail yahooo

We can't use complete feature static content in mail client. It has a limited amount of features.
Common Things:
Won't support javascript
External styles by including the styles
CSS class functionality
Setting background image
Won't consider title tag
hover won't support
iframe not supported
Embedded objects like flash content not supported by mail client
GMAIL headline tag
h1 property 34px
h2 property 22px
h3 property 16px