We'd love for you to read our HTML resources from start to finish (it's chock full of gems, trust us), but if you happen to be short on time, check out these top 10 tips and recommendations for designing emails using your own HTML.
Always build your HTML with tables.
Remove <body>, <head>, <meta>, <title>, <html> or Doctype tags in your HTML.
Use an HTML markup program like HTML Tidy to ensure you've closed all HTML tags.
Don't use image maps.
Avoid colspans and rowspans.
Inline styles are the most solid way to style your emails.
Images should be jpegs or gifs, RGB color values, 72 dpi and double the width of your template (1280px wide).
Always test your mailings by sending to a handful of email programs, or consider using Litmus or Email on Acid.
Include a physical mailing address in the email's footer to comply with Can-Spam.
Don't send one large image in an email.