Here are some steps to help you troubleshoot why your emails are not showing up as HTML format:

1. Check if your email client is using plain-text mode
   
2. Verify settings in your email service configuration
   
3. Check the view in browser option in your email’s sending service
   
4. Confirm you have the most recent version of the email client
   
5. Check your email for undesired content filters (spam, attachment, etc.) set up in your email account
   
6. Verify if traffic ports used by your email client are open (25 or 587 port)