What is the standard size for email greetings cards, birthday cards?
Is there a standard, or best practice size for a greeting card you plan on sending only via email? I saw one post say as long as the width is below 600px
You're right. I'll add a couple of other helpful tips.
The best practice for emails is still to use XHTML 1.0 Transitional doctype and create a tabled layout, usually no more than 600px wide, keeping all HTML styling inline (and avoid shorthand).
Some newer email clients now read the
<style> tag in your
<head>, allowing you to use CSS classes and even media queries, to create responsive emails at whatever size you'd like.
These are a few good resources, with much more information on the subject: