Here are some factors to consider when making an HTML email message:
- Host the images on a Web server
- Use absolute URL for the image links
- Use compressed images (avoiding gradients helps; fewer colors helps)
- Use 90s-era HTML; avoid CSS
- Width should be 600 pixels or less
- Keep the layout very simple, with minimal use of tables
- The layout should be vertical, with minimal use of cells flowing horizontally
- Try to use HTML text for your headline, rather than placing that text on an image
- Send your message to accounts that you've set up with multiple services (Hotmail, Gmail, etc.)
- Have friends help you test the message
- Remember your call to action: is the message linked to a landing page where your recipients may fill out a form or take some other action?
These tips should serve as good guidelines for creating your HTML newsletter. Remember, some in your audience may prefer text messages or tweets over email. Best of luck!