HTML letters are confirmation or promotional letters formatted using HTML (HyperText Markup Language) to include rich text features such as images, colors, links, and styled text. Unlike plain text emails, HTML letters can be visually enhanced and formatted, allowing for a more engaging and visually appealing presentation. Just like with any email, these letters might sometimes fail to be sent. If this happens, you can check the following:

1. Go to Management > Setup > Letters, and make sure the HTML box is checked.

2. Try to re-upload each letter.